In general it makes no difference what breeds or shapes and to some degree sizes make. (size would only matter if there was a risk of injury due to behaviour related to size like squashing).
And yes, all bunnies involved should be spayed/neutered regardless of sex and status of the other buns involved (in all but exceptional circumstances).
Bunnies who are not neutered have been bonded in the past but for the best results and longevity of the bond, all should be done prior to introduction and should have a period of approx 4-6 weeks post op before intros commence. (It has been done sooner, but these are generally held recommendations).