"Happy Birthday Eva and Erika," a crowd of friends and family echo as they sing happy birthday to the twin girls on Saturday.

This birthday wasn't just a standard celebration of another year since their birth, this occasion was a much more important milestone for the twins.

Eva and Erika were born conjoined at the chest and had to undergo a risky 17 hour surgery to separate them.

The girls shared their digestive system, uterus, liver, bladder and a third leg and after their surgery the 2 year olds were able to finally pursue their own separate interests.

Before the operation, Erika was almost half the size of her sister Eva, which caused doctors to fear for Eva's health.

Eva completed the operation with a large intestine, small intestine and colon, whereas her sister Erika only has a small intestine.

The girls were discharged from Packard Children's Hospital a few months after their surgery and have been back at home with their parents behaving like normal toddlers.

"Neither girl seems to have trouble adjusting," said Packard Children's child psychiatrist Michelle Goldsmith, MD, who has worked with the toddlers. "They're both rolling with what's going on very well."

That's why this birthday party meant so much to the family.

This birthday party was an emotional day for both their parents Aida and Arturo Sandoval, because initially they were unsure if the girls would make it to their third birthdays.

"It's a big deal for both of us," Aida said.

When they were in the hospital, their primary focus was to get the girls healthy, so thinking about celebrating days like this didn't even cross their minds.

The party drew in quite a crowd including Erica Keesis-Segura who was with the twins in the NICU in Stanford.

"It was a lot of unknowns and we didn't know how to do things for them and it was a lot of different things. How do we put a diaper on them? How do you hold them? How do we change them?" Erica said.

With plenty of help to heal the girls are thriving now as they spend their first birthday as 2 separate people.

"The amazing moments are those moments when they start to get up on the couch, when they get up on the little horsey they just got. It's the little things," Aida said.

The family is now taking the little wins and looking ahead to the big leaps in their lives.

"We are excited, we are going to start preschool sometime soon, hopefully this year," Aida said. "It's nerve-racking. I know I'm going to cry, but I know it's the best thing for them."

No matter what challenges the girls face in their lives, they still have each other.

"I actually cry when I see them hugging each other," Aida said.

By the looks of their birthday celebration, those are only tears of joy.

Source: CBS Sacramento