I am glad to hear there is not a possible medical issue! That was my biggest fear. I remember watching a show where a brain tumor (in a human) caused aggressive behavior. That kept popping through my thoughts.
Yes, they are all clearly male. (very dark bright blue cere w/no white) (the beginning of my avatar shows a fairly good close up of each.
The mounting thing could be. At the beginning of one of the fights it did look like Antigua was trying to mount Aruba. It happened so quickly and they were locked feet to feet so fast that I wasn't even sure if that was what I saw.
Since I adopted Caico and Antigua from a gal here and she had gotten them from a shelter after another owner gave them up, I honestly am not sure how old they are. She thought they were about a year old when she gave them to me but I'm not sure. That would put them around 2 now. At any rate, they weren't babies. Aruba was around 9 months old when I got him so that puts him also at about 2. Cayman was about 3 months when I got him so he is actually about 1 right now but he doesn't seem to be involved with the aggressive behavior at all.
I'm glad I didn't sell this other cage. The other one I have is just too small for a longer term separation. It's one of those cages that uneducated people (yes, that was me in the very beginning) get for their birds to start with.
I will do what I have to do and keep them apart as long as needed. It isn't going to be easy-I really don't have any good place for this other cage to sit but I'll work it out.
The worst part is that they are all 4 very used to being out of the cage from the time they are uncovered in the morning till they are covered at night. We will work out something though.