In my opinion, rabbits are much happier when they are bonded. However, two unspayed females may be difficult to bond. Please read up thoroughly in our Library on bonding before attemtping to do so. Rabbits have been known to seriously injure and even kill other rabbits.
If they do bond easily even though neither is spayed, they will probably be much happier together. However, once you bond two rabbits it is considered quite cruel to separate them. They will be lost without the other once you bond them. So if you plan on breeding one again it would probably not be a good idea to bond her to another.
Is there a reason why you feel the need to breed them again?