conjoined twin girls sharing a body but with two healthy hy hear hearts. their parents anguish with as one grows stronger and the other weakens. >> you talk to them and say you are strong and you'll get through this. >> could they survive separation surgery? >> knowing the girls and what they've gone through, they're fighters. >> tonight the dramatic decision, the risky procedure with two lives on the line. >> a prayer for. >> lindsey davis on one family's emotional journey. >> was there ever a part of you that thought this might not work. >> and the moment that brought everyone to tears. >> this special edition of

"nightline," becoming two, will be right back.

really? really? really? really? really? see zero in a whole new way. get zero down, zero deposit, zero first month's payment, and zero due at signing on select volkswagen models. now with the people first warranty. announcer: this is a special edition of "nightline," becoming two. from the moment they were born, you couldn't see eva without seeing her sister erica, conjoined twins, they have never known life apart.

tonight we take you inside the complicated and risky surgery to separate them. >> have we anticipated all the potential risks? are we prepared to deal with a bad outcome? >> these two little lives on the line. >> was there ever a part of you that thought this might not work. >> their journey begins in california in the spring of 2014 with three children almost out of the house, 44-year-old ieta sandoval and her husband were looking forward to becoming empty nesters, but little did they know they're about to receive some life changing news. >> i was having pain and then i told art about it and he's like, why don't you go to the doctor, i think it's your ulcer. >> to her surprise, she finds out she's pregnant with not one, but two babies. >> and so what was your reaction? >> whoa. >> shocked. >> shocked. >> i went okay. >> he was pretty quiet. >> we're not kids any more. >> one month later, the doctor

recommend she see a specialist, she assumes it's because of her advanced age. >> he said, you know, we do find some abnormalities, they are twins and they are conjoined. >> conjoined twins are a rare phenomenon, their chances of survival even rare, about half of still born and only 35% survive beyond the first day. >> i think when you're hit with some news like that, he didn't know how to deal with it. i didn't know how to deal with it. you don't know who to turn to. >> reporter: the so the sandoval reach out to gary hartman. >> this is erica's pelvis. >> reporter: an expert in the world of conjoined twins but despite having six successfully separation surgeries under his belt, he says every case presents its own challenges. we told them we didn't know that they could be separated. we weren't real optimistic about

quality of life. >> reporter: doctors gave them the option of terminating the pregnancy. >> reporter: did you ever have a moment where you thought should we do this? >> i didn't. >> reporter: what was it that made you think this is never an option to end this pregnancy? >> i feel it was my faith. >> we talked about it. let's give them a chance, you know. if it's meant to be it's meant to be. >> reporter: after 33 weeks of pregnancy, the sandovals welcomed two baby girls into the world erica rose and eva victoria, they are joined from the sternum to the pelvis. >> they had the tubes and covers over your eyes. you can't carry them, they're very fragile. you question yourself, are we doing the right thing? you talk to them and say you are strong and you're going to get through this. >> reporter: right from the start, they begin to defy the

odds but because they need specialized treatment, they must spend the first few months of their lives in the intensive care unit. >> when those beautiful girls were born, that family was very scared. mom would stand over by the window with the bed many feet away and we would just working with her to come over and touch the dwirlz and to know where she could put her hands in a place that wouldn't hurt them. >> reporter: finally at seven months old, the girls are deemed strong enough to go home to sacramento, despite 24 years as a mother, nothing could have prepared her for this. >> this is her feeding, so we're giving her, her eight ounces is what she's getting erica. >> reporter: even the simply yest of tasks like bath time and putting on clothes become an exercise in patience and creativity. >> these were the little gowns

that were made, trying to keep them dressed, something cute is what i wanted to put on them. >> reporter: and velcro is a godsend, right? >> right. >> reporter: like other kids, they hit all their first milestones, but they do so together. >> hi. >> reporter: from their words. >> up. >> up. >> reporter: to learning how to stand. >> very nice. i appreciate that. >> reporter: not wanting to leave their specialized care, they must make the nearly three hour journey to palo alto regularly for checkups, even during those uncomfortable car rides, the girls remain upbeat. they begin to develop their own personalities, eva, the talkative one, erica, the observer, but eva also becomes stronger and larger than her sister often dragging even

throwing her around. over time their health starts to decline. >> reporter: what's been the most trying time? >> the utis, they're throwing up, they're dehydrated. >> eva. sister's sick. don't bounce. >> the month of july, we were in the hospital just practically the whole month. >> reporter: erica kept getting weaker and weaker. >> she was just basically getting smaller and eva was getting bigger so we really have to do something about this. >> reporter: we concern mounting the family and doctors decide they need to separate the two-year-old girls now. >> were you able to explain to them at their age what was going to happen. >> i would always role play and some magic's going to happen and dr. hartman is going to be your magician. >> reporter: with only 250 separation surgeries successfully performed in the world the doctors tell the sandoval there's a 30% chance one of the twins could die.

was there ever a part of you that thought this might not work? >> a very small part. knowing the girls, how much they've gone through, they're fighters. >> reporter: it's finally the morning of the surgery. the twins are their usually bubbly selves. two hours later when they arrive at the hospital, reality sets in for the msando val, they place their faith in god and their babies in the hands of this team of specialists. the nearly 50 person medical team begins with a prayer for guidance. >> as we work together, a prayer for strength. >> reporter: in a nearby room, the sandovals and dozens of family members join in. >> our father who art in heaven -- >> i felt a calmness come over me that it was going to be okay no matter what, what the outcome

was. >> reporter: after four hours of careful prep, it's now time to begin the separation. >> they made their first incision. >> reporter: the plan is to separate the organs of the chest first. they're hoping that the twins shared leg can be given to erica. as the hours pass the doctors encounter a few surprises. >> erica's small intest inned joined eva's just before the large intestine. >> reporter: and that is problem? >> actually you can be fine with just a small intestine. >> reporter: they continue the delicate dance of dividing the girls organs. >> they were able to split the bladder so they each have a bladder. >> reporter: every step a daunting task, one false move could spell disaster. >> the big challenge is then closing that wound, that's the real risky part. >> reporter: when we come back, ieda and art are given difficult

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announcer: this special edition of "nightline" becoming two continues. >> reporter: 2-year-old conjoined twins ea and eva sandoval are undergoing a tense separation surgery. they have had to carefully coordinate their every move performing a difficult and delicate dance. and then finally.

>> they are two now. >> reporter: the prayers of their parents, art and ieda, are answered. [ applause ] >> reporter: the twins successfully separated but the work of dr. hartman and his team is far from over. >> it seems like the most dramatic piece of the procedure and people are all focused on that but that's just like step 34 of 50 or 60 steps. >> reporter: the surgical team now faces a new hurdle, they realize they don't have enough skin to close the girls wounds, so they turn to their once shared leg they were hoping to give to erica. it's now needed for something more crucial, it's skin tissue. >> they had told us earlier they may have been able to use that third leg and give it to erica but when it came down to it there wasn't enough tissue to cover up erica. >> that was really hard. it's just like a punch in the

gut. >> reporter: but despite that set back the rest of the surgery goes as planned and after a total of 13 hours. >> we're good. >> reporter: the twins are wheeled into recovery. tell me the first time you saw them after the surgery. >> i was excited just to know that they were alive still, just to know -- see them breathing. >> reporter: after spending their first six nights recovering in separate beds, the girls are in the weeks that follow. >> you want a hat? >> yeah. >> reporter: erica the once smaller twin is now thriving. she makes tremendous progress at physical therapy. >> one, two, she has figured out with this

totally new body how to be really mobile really fast. can i put the purple one in? >> reporter: but the road to recovery is not as easy for eva. >> eva, one, two -- there you go. >> so with eva she's had a lot of pain and also anxiety with getting up so a lot of our sessions are focused into getting into more of an upright position. >> do you want to go see eva? >> ever her sister's keeper, erica tries to comfort eva. >> it's okay. it's okay. >> reporter: through it all, ieda is mostly parenting solo. >> with work i could be out on the road all week. >> reporter: art who's had to keep working full time back at home to cover the medical

expenses, drives the three hours every weekend to visit her and the girls. >> i'll do what i have to do to make things work. it's our life and we -- we adjust to it and you keep on going. >> reporter: the hospital becomes like home for the girls who haven't been outside in two months. >> can you see the clouds moving? what do you see in those clouds? >> elephant. >> you see an elephant in the clou clouds. >> look at sister. listen to my voice. >> reporter: finally, after three months in the hospital, a breath of fresh air, an ambulance while often a sign of tragedy and fear, on this day is one of hope. >> all right. you made it! >> got a friend. >> reporter: erica and eva are making the journey home to

sacramento. >> you ready to go? >> yeah, man. >> reporter: in the care of their local hospital, the girls continue physical therapy. >> i want you to push it down. >> hold on to your wheelchair. >> reporter: and are fitted for wheelchairs. >> he'll stay right here with you. there you go. >> i just think it's amazing that we're at this point with them with their lives and feeling sick is not going to hold the other one back. >> reporter: now their free to roam at home. >> i love it. >> reporter: where to are the first time erica can go one way and eva can go the other. what is the best part in all of this? >> i love bringing them home and being a family. >> reporter: mom and dad are settling into a new routine. >> here we go, bye friends. >> reporter: with every scoot or step, they surpass all expectations. >> good job. you want to move your leg

closer. >> reporter: no one was certain they would make it this far. >> this is actually the first that i seen them both standing up like this. >> these girls are as healthy as they can be right now. they've gone way past what i thought they he could do at this time. >> reporter: but they still have many challenges ahead. the girls have been on feeding tubes since birth and are just now getting use to eating solid foods. they're also not able to be fitted for prosthetic legs. but dr. hartman is hopeful one day they can. >> we don't have a prosthesis that would work on a girl who has a complete pelvis, but no hip joint on that side, who knows what we're going to have in five years or ten years. >> so you think walking is not out of the question? >> watching what they can do now, i think anything is possible. >> reporter: the girls are embracing their independence as typical toddlers full of curiosity and mischief.

>> somebody who is supposed to be taking a nap, got down from her crib. >> reporter: but that connection they once shared, never far from memory. >> she will go, my sister was right here and i said, yes, your sister was right there. we do talk about it. >> she did say that. i gave her my leg, she took my leg. >> where's your leg? >> erica took it. >> reporter: after two years living at one, they're about to celebrate their third their first as separate individuals. at a party full of family and friends ♪ happy birthday to you. >> reporter: the girls dress as woody and princess sofia and even though they're on their own, they're still inseparatable. >> i love watching them.

so whether they have a disability or not it's just being with people and doing kid stuff. >> are you ready, erica? >> go, eva. go, go, go! >> reporter: the girls fiercely fighting to be just like any other kids. >> so would you do it all over again? >> i would. >> maybe a little younger. >> i know that god won't give you something you can't handle. there's nothing that these girls can't do. they are fully capable of doing anything. >> reporter: for nightline, i'm lindsey davis in sacramento, california. our thanks to lindsey. we'll be right back. announcer: this special edition of "nightline" is brought to you by jc penny.

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special thanks to the sandoval family. they thought us a lot about faith. hee bruise 11:1 reads. faith is the substance of things

hoped for, the evidence of things not seen. thank you for watching abc news. thanks for the company, america. happy thanksgiving.

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