if they are not neutered i would jsut wait it isnt worth the fights that could ensure either during bonding or even after while waiting for spays also they would all need to go in and be spayed at same time to avoid breakign the bond and not all vets wil lhave facilitys to house 4 rabbits together, best to get all neutered then try bonding in a nuetral area, imagine if they had a fight now then you were unable to bond them once neuereed because you ahd been impatient and tried to do it now.