As conjoined twins in a perpetual hug, Kendra and Maliyah Herrin have shared absolutely everything for the past four years -- including an abdomen, pelvis, liver, kidney, large intestine and two legs.
But soon the 4-year-old girls of North Salt Lake, Utah, will undergo a 30-hour surgery so they can live separate lives.
It was difficult for their mother, Erin Herrin, to decide to put her adorable, giggling girls through such an extensive medical procedure.
"I flip-flopped both ways," she said. "I was like, they're healthy, they're safe right now, we can keep them together and keep them safe, or we can separate them and give them the best chance possible of leading separate lives."
"They seem to … see themselves as being separate when they got older," said Jake Herrin, the twins' father. "They want to be married, they want to be moms."
To emotionally prepare for their separation at Primary Children's Medical Center in Salt Lake City, the twins have been working with a child psychologist, role-playing through their surgery using conjoined dolls that they snip with scissors to separate.
But for Kendra and Maliyah, the real-life operation won't be so simple.
"The dangers of the surgery are tremendous," said Dr. David Staffenberg, chief of pediatric plastic surgery at The Children's Hospital at Montefiore in Bronx, N.Y., who separated conjoined Filipino twins Carl and Clarence Aguirre in a 17-hour operation.
When the twins separate, Kendra will get the kidney while Maliyah will have to spend months on dialysis, waiting for a transplant. That's one of the reasons why the twins have waited to do a surgery that is usually done much younger -- to improve Maliyah's chances for a successful transplant.
"To even be considered for separation in the face of a shared organ like a kidney, where one of the girls would have to go out until she could receive a transplant, is really unusual," Staffenberg said.
The hope is that their mother will be a match and will eventually give her daughter a second gift of life.
"I'd donate both my kidneys if that meant that she would be able to live a healthy, normal life for the rest of her life," she said. "I'd do anything for my children. I think most mothers would."
Each twin will get one leg -- they each control one now. Their parents said they hope that with crutches or prosthetics, the girls will be able to walk.
It's not as if they haven't beaten the odds before.
ABC News' Taina Hernandez reported this story for "Good Morning America."