Since you mention it is a problem specifically with the hairless, I would consider that being your problem. Some lines and types of true hairless (distinct from rex and double rex) do have problems lactating.

If you want to get rid of a male, get rid of the aggressive one first. I would recommend keeping at least two males - so if something happens to one you still have another ready to breed. This is ideal in any breeding program. Periodically you'll want to replace one or both males too, with something better and younger.