I read that a rabbit will sometimes nurse another's babies if they're snuck in with her litter. However, if the two females are both present and both want to nurse, I'm not sure if they'll share the same nest.
I have two does and one buck, I separated the two females and put the male in a separate cage recently because I was worried about them mating. In the short time together out of the cages, it seems the male still managed to impregnate at least one of them. I don't know who gave birth to the first litter, because I wasn't in the room. I separated the two females and put who I thought was the mother with the kits, but within a day the one I removed from the kits gave birth. I don't know what to do, so I connected the two cages again, putting both females back together, and I placed the new litter in with the previous one, in the nest I watched both rabbits build up to the birth. I'm going to buy a syringe and formula just in case I've made a poor decision. I will watch them for any kind of violence as well. I hope you figured out what to do with your rabbits. I read that a syringe and some formula can be used if it doesn't seem to be working.