Putting all males in one small tank sounds like a warzone to me. I expect all livebearer males to "not" get along unless there are an adequate ratio of females.
BTW I have a ton of guppies as their offspring now and they get along well, with all my fish, I have sceen 2 of the older males chase each other a bit, but usualy they are swimming with each other chasing the girl. Waiting for some of the girls to get older to clean up my ratio.
Luckily my girl is 2 times as big as my largest boy so she can fend them off most of the time if she is not in the mood.
I could be wrong, but I don't think that they actually "have sex". I don't think the gonopodium is actually inserted into anything. It just touches the females opening and releases a packet of sperm.
I could be wrong, but from what I have seen that is what happens.