Barreto has a 13-year-old daughter and a 10-year-old son, and said she knew what a huge gift she was giving to the Hamlets.
"I just did it to give them the gift," she said. "You know, I just, I just felt like if I can take ten months out of my life and give them a lifetime of a child, then it's worth it."
"It wasn't as hard a decision as people think. I mean, for me, it wasn't," she said. "When you are becoming a surrogate, this is not your child. You're just carrying it. They needed help."
"She's a strong lady," Hamlet said of her sister-in-law. "I knew that. And she loves her family very much."
The doctor implanted two embryos in Barreto, who said she hoped to give the couple twins and complete their family.
"You know, this way they -- they wouldn't have to think about having another child," she said. "They would be done and that would be it."
And despite the risk of the cancer returning, Hamlet had two embryos implanted in her as well. It was a long shot, but she took the chance.
"We were at the point where [we thought] at least we'll get -- maybe we'll get one out of the four," Barreto said. "I mean, what's the chances of not getting one out of the four?"
Both women became pregnant, but they didn't tell the whole family until they were four months along. When friends asked Barreto about her pregnancy she immediately told them she was a surrogate -- "the oven" -- for her brother and his wife.
Hamlet and Barreto's pregnancies were parallel in every way: they would chat on the phone about feeling sick, swollen feet and which babies were breech.
And those names that all begin with the letter M was also something they did together.
"I felt like there was so much sharing in the very beginning, that I had to share back with the names," Hamlet said.
The babies, who are fraternal quadruplets, were born 10 days apart in June. Hamlet gave birth first, to Michael and Michelle. Barreto then gave birth to Madison and Marissa.
"She was in the operating room when they delivered the two that I was carrying, and she kept saying, 'Oh, I don't know how, like, I can thank you,'" Barreto said. "And I'm like, 'You know, just take care of these babies. That's all -- that's the way you should thank me."
The Hamlets are six weeks into parenthood, and loving every minute -- times four.
"I said, 'Anne Marie, you know, when they all cry, you're going to be going out of your mind,'" Barreto said. "She's like, 'You know, Marlo, what I went through, it's music to my ear, when you hear those babies cry. It's just music.' And she hasn't complained yet."
Hamlet says she looks at her children and "can't believe" how lucky she is.
"They're so beautiful," she said. "We just never gave up."
"You could see their faces light up, looking at those kids," Barreto said. "You do. I mean, they're like laughing, when their kids are crying. They're laughing at it, you know? Dream come true."