You need to spay the female (shes the older one?) or else she will get pregnant. You need to then neuter the male to get rid of the hormones because having one bun altered and the other not is a mess of weird smells for both of the buns, and they will most likely fight, and not bond.

Most importantly though, keep them apart until one is altered (they should do this at around a year I think, but you should go to the vet and see what they say) and then for a few weeks afterwards (as they can get really hurt if they fight after surgery, and the male is still able to get the female pregnant (if it was him you alter) for a bit after the surgery… But you dont want to have babies… After they are altered, it should be relatively easy to bond them, as they are related, and you have a male-female pair.

Good luck.

(Also I cannot believe they had two litters in such a short time frame — you said they are only a few weeks apart? — , if this was on purpose, this is very harmful to the mommy.. After having two litters alone that mommy should be put out of commission… If it was an accident they should get her spayed/the male neutered as well…. )

That’s good. (And yes they can basically get pregnant as soon as they have the babies)

Do you have two separate cages/living spaces for your buns for the time being? I am afraid they cant be together… Even at a young age it only takes one mounting to get the female pregnant, which as you have witnessed, only takes a few seconds. Buns need to be able to run around, and so if they have separate cages (or a way to let them out one at a time), they can take turns out in the room…