They were born in Guatemala and brought to the U.S. in 2003 to be surgically separated at Mattel Children's Hospital in Los Angeles.
Doctors say Josie and Teresita are defying the odds because there are few cases of successfully separated conjoined twins.
However, it hasn't been easy, especially for Teresa, who had many more medical obstacles than Josie. Last year, Teresa developed a severe brain infection that nearly killed her.
"We were really scared because we thought she was going to pass away, but she's fine," said Werner Cajas, who is part of Teresita's host family. "She's a fighter."
Teresa lives in Santa Clarita with Cajas and wife Florie. Although Teresa was declared legally blind and deaf, the couple says they know she can see, hear and sense the world.
"The first time she smiled we threw a party," Werner Cajas said. "The most beautiful smile in the world for us."
Both girls bring joy to their families. Josie is about to enter fourth grade and lives in La Canada with her host mother, Jenny Hull.
The sisters see each other twice a week, but their sisterly bond is closer than most. They see their birth parents twice a year and talk every Sunday.
With the help of Mending Kids International, the group that brought them to the U.S. from Guatemala, the two families are able to give the sisters the intense medical care they need.