"I wanted to be a member of that club so badly, and now I'm in and it's so much better than I even imagined," Cross, 45, tells PEOPLE in its new issue.
She's also settled into the schedule all new moms know by heart. "I'll tell you my routine – it's really exciting, " she says with a laugh. "I feed, I burp, I change diapers, I pump. And then I have a tiny window of time to myself."
The routine is welcome for the actress and Mahoney, 49, who wed in June and weren't sure they'd be able to have kids. "We did in vitro a week after we got married," she says. "We were supposed to go to Greece and Paris and have this fancy honeymoon, and I said, 'Let's stay put and see if we can't give this baby a chance.' "
It worked – times two. But four weeks before her March 21 due date, Cross was diagnosed with preeclampsia, a disorder characterized by dangerously high blood pressure that threatens both mother and baby. Within hours, she gave birth via cesarean section to Savannah (6 lbs. 7 oz.) and Eden (5 lbs. 10 oz.). "I had over 12 lbs. of baby in me!" she notes.
REGINE MAHAUX / EXCLUSIVE BY GETTY
Looking ahead, she doesn't rule out more kids – "I'm probably done," she says, "but I certainly can see why people keep going" – but for now she's enjoying the moment: "I'm in heaven right now."
For more exclusive photos, plus how Marcia picked her babies' names and made it through nine weeks of bed rest, pick up the new issue of PEOPLE, on newsstands Friday.