Growing up, identical twins Jill Justiniani and Erin Cheplak did just about everything in sync.
"We played together, slept together, ate together," Jill, 30, of Yorba Linda, California, tells PEOPLE. "My parents would talk about how we had our own language together. We'd be in our cribs side to side and make these cooing sounds. I'd make a sound and Erin would respond."
Now, they've become parents together — on the same day, in the same hospital, within hours of each other.
On May 5, both sisters welcomed sons, with each baby weighing 7 pounds, 3 ounces, and measuring 20 inches.
courtesy Jill Justiniani and Erin Cheplak Erin, left, holding Silas and Jill, holding Oliver
"It just feels like it was supposed to be," says Jill. "It is a little surprising because what are the odds? But it's like, of course, this would happen to us."
While the sisters planned on getting pregnant at the same time — "We've always said that it would be very fun for us," says Erin — giving birth on the same day had not crossed their minds.
Jill was scheduled for a cesarean section at the Kaiser Permanente Hospital in Anaheim on May 5 because doctors discovered her son, Oliver, was in a breech position. Erin's baby, Silas, was due on May 15. But on the morning of May 5, Erin's water broke.
courtesy Jill Justiniani and Erin Cheplak Erin and Silas, left, with Jill and Oliver in hospital
"I called my husband, Zach, and I said, 'Okay, this isn't a joke. My water just broke. I'm going to need you to come home from work and take me to labor and delivery,' " she recalls.
"My next phone call was to Jill and I said, 'Okay, this isn't a joke, but I'm pretty sure my water just broke.' Jill's like, 'All right. Well, I'll see you there.' "
Kaiser Staff From left, Zach, Erin, Jill and Ian at the hospital hours before the babies were born
Jill's procedure was scheduled for 1:30 p.m., but was delayed due to a few emergency c-sections at the hospital that day. Meanwhile, Erin arrived at the hospital at 9:30 a.m. and was soon in active labor. Jill and her husband, Ian, joined Erin and her husband, Zach, in their room for hours.
"It was the four of us and all being a support system together," says Erin. "They were there for my strong contractions, I could not have gotten through that without that support."
Oliver was born at 6:39 p.m., and Silas followed at 11:31 p.m.
Then, the couples got another surprise.
"We knew Oliver's numbers. I was just kind of, "Okay, cool. It's a pretty big baby,' " says Zach, 34, who is also a twin.
"Then the nurse did Silas's weight and length. Exactly the same. 'I said, 'You got to be kidding me,' " he continues. "It was just incredible."
Bethany Jean Photography Jill, left, and Erin
Erin, Jill and their babies had rooms across the hall from each other. After being discharged at the same time, they each returned to their homes — located just five minutes apart in Yorba Linda.
"It's such a blessing being so close," says Erin, who had been living about 45 minutes away in Long Beach when she discovered she was pregnant.
She and Zach moved to Yorba Linda so that the children could grow up together.
"Being identical twins, Jill and I know no difference, other than spending all of life's journeys together," says Erin. "It's an experience that has been amazing and it's something that Jill and I cherish so much.
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"We're each other's best friends and to know that our sons are going to grow up with the opportunity for a similar experience is a huge blessing," she continues. "We're so grateful for that."
courtesy Jill Justiniani and Erin Cheplak Jill, left and Erin as infants
Raised in nearby Brea, California, the twins were six when their younger sister, Allison, was born with a rare genetic disorder that required many medical appointments and hospital stays.
"We watched my parents navigate raising a disabled child but also raising us as well," says Jill. "Erin and I, we always had each other to lean on. And that also bonded us.
"That's just another really special thing for our sons — they're going to have a sense of closeness that they can also rely on each other the way that my sister and I did," adds Jill.
courtesy Jill Justiniani and Erin Cheplak Zach, Erin and Silas
Allison died at 12, and the twins' experiences with their sibling led them to study occupational therapy with a focus on helping children with disabilities.
They now work together as pediatric occupational therapists in an outpatient clinic. "It's really shaped our career, our passion and our focus," says Erin.
courtesy Jill Justiniani and Erin Cheplak Jill, Ian and Oliver
Ian met Jill in high school, and the pair married in August 2019. "Growing up with them, when they say that they're each other's best friends, when they say that they lean on each other," he says, "they really, really do."
Meanwhile, Erin and Zach, 34, got married in a small ceremony in October 2020, but due to the COVID-19 pandemic, they delayed having a big celebration until August 21, 2021.
The morning of the shindig, "Jill called me and said 'Oh my God, you're never going to believe it but I'm pregnant,' " recalls Erin. "Nine days later on our honeymoon in the Maldives, we found out I was pregnant."
Bethany Jean Photography From left, Zach, Erin, Jill and Ian
The couples have lots of help, with Ian's mother living with them while the twins' parents are just 15 minutes away.
Already the babies — who are genetically more similar to half-siblings than first cousins due to the fact that Erin and Jill are identical twins — have started bonding, enjoying visits together just about every day.
"This brings such joy to us," says Erin, "and I'm so happy to share it with others."