Clearsight is known for having amazing foresight and being able to see all the futures, which is only one power, which means she could only be born on one moon, right?

Well, I don't think so. I think the reason why she had very powerful powers was because she was born on two moons (or three), and instead of getting multiple powers she just got one very powerful power.

Darkstalker and Clearsight are probably the same age, so who knows, maybe they were born on the same night.