CHICAGO (CBS) — Baby brothers from Illinois who were born conjoined at the top of their heads face a long road to recovery after they were separated by surgeons in New York overnight.

Doctors in the Bronx successfully separated Anias and Jadon McDonald early Friday, following about a nearly daylong surgical procedure.

The 13-month-old boys were born conjoined at the head, and shared about an inch of brain space. Their parents, Nicole and Christian McDonald quit their jobs in Illinois and moved the family from southwest suburban Braidwood to New York City in February to prepare for the risky procedure.

In a Facebook video posted by CNN before the surgery started, Dr. Sanjay Gupta explained why, despite the risks, the rare surgery was necessary.

“What you will read is that if children who are craniopagus – who are joined at the head – are not separated by the age of 2, about 80 percent of them will die,” he said.

Jadon and Anias are only the 59th set of cranially conjoined twins to be separated.

They were separated after 16 1/2 hours of surgery, at which point surgeons operated on each boy individually to rebuild their skulls. While it took about four more hours before Jadon was sent to a recovery room, the operation for Anias took much longer — more than 10 hours.

Both boys were in pediatric intensive care. In all, more than 20 medical professionals took part in the surgery.

Their mother, Nicole, said despite their sons’ condition, the boys always have been incredibly cheerful and full of life.

“They’re beautiful. They are,” she said. “They’re perfect. They are so funny, and they’re happy. They’re crazy, crazy. Jadon tries to roll off the bed, and drag Anias with him. Anias talks. My favorite thing is to sit here and hear them talking with each other down the hallway. They talk back and forth and they … They’re just, they’re beautiful.”

Before the surgery, Gupta said he doesn’t expect the boys to experience cognitive issues often associated with this type of procedure.

“Were they not conjoined, they seem developmentally normal. I mean, these are just adorable little boys. They’ve got incredible personalities,” he said. “One of the biggest concerns will probably have more to do with motor strength, rather than things like memory or overall cognitive function.”

Nicole posted about the surgery on Facebook on Friday, expressing her joy that the boys have been separated, and her anxiety at what the future holds, as it’s not yet clear what impact the surgery might have on the boys’ cognitive abilities.

“I should feel so happy…TWO SEPARATE BABIES!!!…and yet I ache with the uncertainty of the future,” she wrote. “We are standing on the brink of a vast unknown. The next few months will be critical in terms of recovery and we will not know for sure how Anias and Jadon are recovering for many weeks.”

Nicole said doctors have told her Anias might not be able to move one or both sides of his body after the surgery, and doctors will be monitoring him for possible brain swelling or stroke.

“The plan is to keep them both intubated for about a week…to get through the swelling and pain of the first week…and then go from there. So we just took a huge leap of faith, but now we are back to taking baby steps. In fact, I’m pretty sure I’m still frozen in space and time…in the smiles of yesterday morning. I’ll be hanging out there until I see those smiles again,” she wrote.

Twins conjoined at the head occur approximately once in every 2.5 million births.

The McDonalds have set up a gofundme page to raise money for the medical expenses.