Jake and Erin Herrin pose with their conjoined twin daughters, Kendra, left, and Maliyah, outside their hospital room Thursday at Primary Children's Medical Center in Salt Lake City. The twins say they like being together all the time, but are excited to have separate lives.

Salt Lake City ? They were born in a perpetual hug, their little bodies fused at the midsection so that they are practically face-to-face, and have grown into outgoing 4-year-olds who chatter away and finish each other’s sentences.

Kendra and Maliyah Herrin say they like being together all the time, but they are also full of plans for separate lives. They want to walk without using their wheeled walker, sleep in bunk beds and ride bikes.

“I want to have a princess bike,” Kendra said. “I can go fast.”

On Monday, surgeons at Primary Children’s Medical Center will try to separate the twins in an operation that could take 14 to 30 hours.

The sandy-haired, blue-eyed girls share one pair of legs, a liver, one functioning kidney and part of the large intestine. If all goes according to plan, each girl will get one leg and Kendra the kidney. Maliyah will be put on dialysis until she is strong enough for a kidney transplant from her mother, Erin Herrin.

Dr. Rebecka Meyers, the hospital’s chief of pediatric surgery, said she believes this will be the first time separation surgery has been attempted on twins with a shared kidney.

Conjoined twins occur about once in every 50,000 to 100,000 births. Only about 20 percent survive to become viable candidates for separation, and most separation surgeries occur when the twins are 6 to 12 months old.

“The reason for that is partly psychological, partly mechanical,” Meyers said. “If Maliyah had had a kidney, these girls would have been separated a long time ago.”

Before deciding to go ahead, doctors and the girls’ parents – who also have a 6-year-old daughter and 14-month-old twin boys – talked with ethicists, because the surgery could make things worse for Maliyah, who faces an organ transplant.

“We have more than one ethicist who thinks these girls don’t need to be separated,” Meyers said.