Adding more hens will not help the two 2-year-old roosters get along and stop fighting. Adding more hens will not stop over-mating, barebacked hens, or anything else like that, especially with mature males like you have. If you really want more hens you can use any of this as an excuse but it's not a legitimate reason.
Many people keep males in bachelor pads, no females around. They usually get along well, not any worse than an all-female flock. But if you add one or 25 hens they tend to fight until they determine who is boss. You say it's not bad, that isn't that unusual but sometimes it can be a fight to the death. You can never be sure what will happen. Glad yours are doing OK.