You do have your hands full with these cockerels. There is no law that says cockerels must have full access to hens. They can be kept separate from the hens without any chicken being deprived of well being. As long as there are no hens in with them, cockerels usually get along without much fighting.
If you don't realize it, a hen gives permission to be mated. It may appear that a rooster or cockerel is overpowering a hen, but that is not happening. In the split second in which mating occurs, the hen squats, signalling her receptiveness. It happens so quickly, we don't notice that he's the one taking cues from the hen, not the other way around.
In deciding which cockerels to keep for breeding, watch very carefully for this receptiveness on the part of the hens. Any cockerel that succeeds in mating only after a flamboyant chase and a lot of squawking and commotion, is not good rooster material.