Conjoined Sisters Fused at Waist to Be Separated Next Month Ximena and Scarlett Hernandez-Torres have a third identical triplet sister.

 -- Doctors at a Texas hospital are mapping out a plan to separate conjoined infant sisters who are fused at the waist.

Ximena and Scarlett Hernandez-Torres are scheduled to undergo surgery next month to be separated. The conjoined sisters were born with a third identical triplet sister Catalina, who was not conjoined. The 10-month-old sisters were first detected to be conjoined when their mother, Silvia Hernandez, was just three months pregnant. She told ABC News that the girls have already shown different personalities even though they are not even a year old.

"Scarlett likes to dance, sing and she smiles a lot," Silvia Hernandez said through an interpreter today. "Ximena is most of the time sleeping but she smiles a lot."

The girls are conjoined at their waist and share a colon and bladder, according to the Driscoll Children's Hospital. The operation to separate them is expected to take 12 to 18 hours with specialists from urology, plastic surgery and orthopedics there to help the girls remain healthy.

“A dedicated team of specialists has been working for months to prepare for this complex surgery,” said Dr. Haroon Patel, pediatric surgeon at Driscoll Children's Hospital, in a statement to ABC News today. “This is an extremely challenging operation, but we look forward to a successful outcome.”

A special scanner called a "spy camera" will be used to help doctors understand the complicated blood flow in the girls and to help them stay healthy during the long ordeal. A 3-D model from a specialized MRI will also be used to help doctors map out exactly how to perform the surgery.

“The babies have been doing very well as we’ve focused on getting them healthy for this complex procedure,” said Dr. Miguel DeLeon, medical director of Driscoll’s Neonatal Intensive Care Unit, in a statement to ABC News. “Each member of our team has a well-defined role, and our ultimate goal is to give these two girls the opportunity to live healthy, normal lives.”

Hernandez said she's hopeful for the surgery but still has reservations.

"I have fear of what could happen," she said. "I do have to believe in God's will and that everything will be fine and he will be there in the day of the surgery and he will make a miracle with them."