Male rats rarely have problems living together. I have about 8 together in one cage and 3 in the other cage, and everyone is fine.

Get 2 boys, like your original plan, since your females surely don't need to be bred back to back(being pregnant while nursing, not cool..). Just rotate everyone around so one female is resting or pregnant while the other is nursing, etc. I'd get 3 females though, so the resting female can have a buddy and isn't alone.