Do you know how long they have been neutered for?
Sometimes a new environment or changes to an old one causes stress and fighting. If you have other rabbits or other pets, this could certainly be a trigger also.
You could contact the old owner to find out any specific personality traits that might have been the trouble.
In November I looked after a friends rabbits that always lived in a group. Unfortunately some fights broke out at my place. They did settle again once they went home.
I think separating was wise but try keep them close by one another. You will likely need to do daily bonding sessions with them. The bathtub works well as they have little choice but to acknowledge one another, even if it means ignoring each other. You could try giving them food to share during their bonding sessions.
Hopefully keeping up their interaction and their becoming accustomed to their new home, you should start to see an improvement.