Have you read on their breeding at all? You can't house a pair together.

And where did you get your fat tails from? If same age when you got them, they can be siblings. If siblings then better not breed.

You have to watch carefully at the pair. If you put them together for too long, the female will be very aggressive to the male when she's pregnant. If you don't pay enough attention, she might even kill the male. But like I said, there is a chance that they may be siblings, as there are not many fat tails in the pet trade and I've seen a lot of ppl selling in pairs, not caring if they're related or not. They are not easy to breed, so do consider before doing so.