How did Rome get pregnant?

Well, duh. But why was she ovulating? She told Rei that Vuduri women controlled their ovulation and only became pregnant when the Overmind informed them it was time.

Rome was only partially right. The Overmind had a hand in when a Vuduri woman ovulates but also not having sex was a big boost towards controlling who got pregnant. The relationship between Rei and Rome in Rome's Revolution was not a part of the Overmind's plan.

It turns out that without the Overmind, a Vuduri woman has a monthly cycle and Rome got pregnant without realizing it was possible. Of course after she found out, she was rather pleased. As we found out in Rome's Evolution, since she was part of the Overmind's Slayer experiment, it had not yet given her permission to give birth and privately she suspected she never would be. The fact that she and Rei were charting new territory with the mix of Essessoni and Vuduri gave her the freedom to have a child whenever she was ready and I guess she was ready for Aason.

What about Lupe?