The Baltierras, now happily four months married after dating for 10 years, have seen many ups and downs, including the bittersweet choice to give up their firstborn, Carly, for adoption more than six years ago on Teen Mom and, more recently, the birth of second daughter Novalee Reign on Jan. 1, 2015.
Perhaps the biggest high of all, though, was the girls' first chance to get to know each other as sisters.
While planning the wedding, 23-year-old Catelynn tells PEOPLE she was battling severe postpartum depression (a surprising development since she hadn't shown any signs of depression after Carly's birth). But one sunny day out with her girls was just what she needed to remedy her panic attacks.
"We went to the beach so we were feeding ducks with bread," Catelynn says of the easygoing afternoon. "Carly just wanted to hold Nova immediately and be like, 'Can I feed her? Can I hold her?' "
She tells PEOPLE that Carly "kept showing Nova to everybody and saying, 'This is my birth sister.' It was so cute!"
Says Catelynn, "After that day, I felt perfectly fine again."
While Catelynn and Tyler's adoption agreement has been a source of tension with Carly's adoptive parents, the four have reached a happy understanding. "As long as I get to see her face and hear her voice, hey – I'm sad that I can't share everything, but our story's still out there," says Catelynn. "And people are still learning about adoption, and you guys get some time to see her, and I get to see her, so it kind of works for both of us."
That accord also meant that Carly, Brandon and Teresa were able to share in one of the most touching moments of Catelynn and Tyler's wedding day.
"I was sitting in the room [before the ceremony], and Teresa came in there, just by herself, and she said a few things to me," she recalls. Carly and her parents "got to see me before anybody else, so that was definitely a special moment."
And Carly's little sister has been just as much a source of joy back home in Michigan where the Baltierras live. She says the toddler, who will celebrate her first birthday this weekend with a Minnie Mouse-themed birthday and a "smash cake," has been a unifier for the entire family – including Tyler's father Butch, who is clean and sober after four years in prison – "because everybody just adores her, and we all want to do great things for her."
Teen Mom OG returns Monday at 10 p.m. ET on MTV.