WATCH: Irish American conjoined twins thriving after separation surgery

Erin and Abby Delaney are back home in North Carolina after a lengthy hospital stay

A set of Irish American twins are thriving following a successful surgery to separate them after they were born conjoined at the skull.

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Abby and Erin Delaney, now 2 years old, were born attached at the skull via bone and tissue. The condition, known as Craniopagus, is exceedingly rare and occurs only once in every 2.5 million live births and represents only 2%-6% of all conjoined twins.

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Heather and Riley holding Erin and Abby (Delaney Twins, Facebook)

In June 2017, the girls underwent separation surgery at The Children's Hospital of Philadelphia (CHOP) at only 11 months old. Parents Heather and Riley Delaney chose CHOP as it had previously separated 23 conjoined twins, more than any other hospital in the Western world.

Erin and Abby, however, were the first twins to be separated at CHOP who were conjoined at the head.

While the 11-hour surgery was a success thanks to a team of dedicated doctors and nurses, as well as advanced technology, the road to recovery was long - 485 days long, to be exact.

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Now, though, the Delaney twins are back home with their doting parents Heather and Riley in North Carolina, and mom Heather says her daughters are “are doing so good.”

“It seems like every week they are doing something new and exciting.”

Erin, who Heather lovingly describes as “a little crazy person,” has just started crawling and pulling herself up onto things.

Abby is “finally sitting,” which Heather says “is a huge thing because you don’t know if they’re going to walk until they’re sitting.”

Heather says she’s most looking forward to seeing her twins walk. “I can’t wait to be able to see them run around with the other kids and not seem like they’re any different."

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The family still has to travel to CHOP every three or four months. The journey is long, taking about 10 hours each way, but Heather says that seeing her girls smiling and giggling makes everything worth it.

While the twins are healthily progressing, it is not without cost. The Delaneys have an active GoFundMe to help lessen the costs of the girls' medications, physical therapy, occupational therapy, speech therapy, feeding therapy, play therapy, and music therapy.

Further down the road, the girls will undergo reconstructive surgery. As Dr. Jesse Taylor of CHOP notes, the each of the girls are perfectly fine to live for the time being without their full skull intact, but as they get older and more physical, doctors advise on filling in the gaps.

For now though, Heather and Riley are focused on letting their girls progress naturally and enjoying every moment they can with Abby and Erin.

CHOP recently shared a video on Abby and Erin Delaney's progress: