Twin sisters who were born conjoined at the chest and stomach and who spent nearly six months in the hospital have reached new milestones.

JamieLynn and AmieLynn Finley celebrated their first birthday this month and took their first steps.

"They don't sit still anymore," the sisters' father, James Finley, told "Good Morning America." "They are busy ... they wake up at 6 in the morning and they are ready."

It was just nine months ago that JamieLynn and AmieLynn survived a rare and complex 11-hour surgery that involved separating the girls' liver as well as their skin and fascia.

 

Amanda Arciniega and James Finley hold their conjoined twin daughters AmieLynn and JamieLynn prior to separation surgery.

Following the surgery, the girls spent several more months in the hospital before being able to go their family's home in Saginaw, Texas, for the first time in their young lives.

JamieLynn returned home in March, one month before AmieLynn. The sisters have done nothing but make progress, according to their parents and medical team.

"I just think it's so crazy because they had just got home not too long ago and now they're just thriving," the girls' mom, Amanda Arciniega, told "GMA," adding of their affection for each other, "They always like to touch each other and hold each other's hands and Jamie likes to give Aimee kisses."

 

Twin sisters AmieLynn and JamieLynn Finley are pictured in Dallas Cowboys' jerseys.

Finley added, "When they kiss each other, they giggle and their beds are right next to each other, so when one wakes up, she wakes up her sister."

The sisters also have a shared favorite movie, Disney's "Moana," which was the theme for their birthday party when they turned 1 on Oct. 3.

"They love the music," said Finley, who dressed up as Maui, one of the movie's main characters, for the birthday celebration. "It just like stops them in their tracks when the music comes on."

James Finley, in costume as Maui from the movie

The fact that JamieLynn and AmieLynn were able to be home and celebrating their shared first birthday by walking, dancing and eating birthday cake on their own, in separate high chairs, was a miracle not lost on their parents.

Finley said he thinks about how lucky his family is every time they attend follow-up medical appointments at Cook Children's Medical Center in Fort Worth, where the girls underwent the separation surgery and where they spent their first months of life, in the hospital's neo-natal intensive care unit.

"We were at Cook’s today and I saw somebody with a blue band on and that means they’re in the NICU and I was like, "I’m praying for ya’ll to go home,'" Finley said. "Everybody that's in there, they all want to go home and we made it home, with both of them."

Only a small handful of conjoined twins -- which occur once in every 50,000 to 60,000 births -- survive past birth, according to Dr. Jose Iglesias, medical director of pediatric surgery at Cook Children's Medical Center and the lead surgeon for the twins' separation surgery.

Dr. Mary Frances Lynch, the neonatologist who cared for JamieLynn and AmieLynn in the NICU at Cook Children's, told "GMA" that the twins' progress has been "amazing."

"They are just right on target with their developmental milestones. They're very social," said Lynch, also medical director at Pediatrix Neonatology of Texas. "They’re even a little ahead of schedule as far as their motor skills are concerned, so it's really just incredible."

Lynch said doctors are continuing to closely monitor JamieLynn and AmieLynn, who is also being treated for scoliosis, but the expectation is that they will go on to lead healthy lives.

"It's so gratifying for everybody who was involved in their care -- nurses, occupational therapists, physical therapists, speech therapy, respiratory therapy, all people that were so involved with, with these girls and their family," she said. "When they come visit, just seeing people flock to come and see how they're doing, it just really warms your heart and it reminds everybody why we why we do what we do."

Lynch noted that over the many months she and other doctors and nurses provided care for JamieLynn and AmieLynn, they also got to see firsthand the incredible love and care the girls received from their parents.

"I can't say enough about how wonderful their parents are," she said. "They're just an amazing, amazing family those girls are very blessed to have such wonderful parents and family around them."