Transcript for Conjoined twin girls undergo risky separation surgery: Part 2
??? 2-year-old conjoined twins Erika and Eva Sandoval are undergoing an intense separation surgery. The past five hours, 13 surgeons at Lucille Packard children's hospital have had to carefully coordinate their every move, performing a difficult and delicate dance. And then finally -- They're two now. Reporter: The prayers of their parents art and 8 deaida are answered. 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 that once-shared leg they were hoping to give to Erika. It's now needed for something more crucial, its skin tissue. They had told us earlier that they may have been able to use that third leg and give to it Erika. But when it came down to it, there wasn't enough tissue to cover Erika. That was really hard. You know, it's just like a punch in the gut. Reporter: But despite that setback, the rest of the surgery goes as planned. And after a total of 13 hours -- Okay, we're good. Reporter: The twins are wheeled into recovery. So tell me about the first time that you guys saw the girls 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 reunited. In the weeks that follow, Erika, the once-smaller twin, is now thriving. She makes tremendous progress at physical therapy. One, two, three! She has figured out with this totally new body how to be really mobile really fast. 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, also anxiety. So a lot of our sessions are focused on trying to get her in more of an upright position. Do you want to go see Eva? Yeah. Reporter: Ever her sister's keeper, Erika tries to comfort Eva. It's okay, it's okay. Reporter: Through it all, Aida is mostly parenting solo. I was working. I could be 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 adjust to it. And we 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 the clouds? Elephant. You see an elephant in the clouds? Here we go. Outside. Outside. Mama? I'm right here. Look at sister. 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! Look at you. Reporter: Erika and Eva are making the journey home to Sacramento. You ready to go? Yeah. Reporter: In the care of their local hospital, the girls continue physical therapy. Hold on to your wheelchair. Reporter: And are fitted for wheelcha wheelchairs. There you go, see? I just think it's amazing that we're at this point with them in their lives, you know. And feeling sick is not going to hold the other one back. Reporter: Now they're free to roam at home. I love it! Reporter: Where for the first time Erika can go one way and Eva can go the other. You guys play so nicely together. What is the best part in all of this? I love bringing them home and being a family. Their smiles. Reporter: Mom and dad are settling into a new routine. Here we go. Bye, friends! Reporter: With every scoop 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've 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 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 used to eating solid foods. They're also not able to be fitted for prosthetic legs. But Dr. Hartman is hopeful that one day they can. Yeah, we don't have a prosthesis right now that would work on a girl who has a complete pelvis, but nothing, no hip joint on that side. Who knows what we're going to have in five years or ten years. You think walking is not out of the question? Yeah, 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 was supposed to be taking a nap got down from her crib. Reporter: But that connection they once shared, never far from memory. Eva will see her, she goes, my sister was right here. Yes, your sister was right there. We do talk about it. "She took my leg." She did say that, "She took my leg." Where's your leg? "Erika took it." Reporter: After two years living as one, they're about to celebrate their 3rd birthday. Their first as separate individuals. I'm going to be woody! Reporter: At a party full of family and friends -- ??? happy birthday to you ??? Reporter: The girls dress as woody and princess Sofia. Some ways they're still inseparable. I love watching them. They know that all these people are there and they're going to play with them. Whether they have a disability or not, it's just being with people and doing kid stuff. Are you ready? Go, go, come on, Eva, go, go, go! Reporter: The girls fiercely fighting to be just like any other kids. Would you do it all over again? I would. Yeah. Maybe a little younger. I know that god won't give you something you can't handle. There is nothing that these girls can't do. They are fully capable of doing anything. Reporter: For "Nightline," I'm linsey Davis in Sacramento, California.
This transcript has been automatically generated and may not be 100% accurate.