I know a guy who keeps 4 males in the same tank, and its about half the size and not planted like yours jude, They are related to the piranah family, but i havnt found them aggressive, and ive watched these fellas in his tank and they dont hassle each other at all, if anything i would say they enjoy each others company. Ive also heard of alot of ppl keeping more than one male in a tank, This is something i will be trying in my fishroom. I couldnt say no to having those sortta colours together in a tank. However others will tell you NO do not mix, Its up to you.
Yes the males can become aggresive when tending to his nest, if you have female and they make a nest, you can fix the aggresion problem by removeing the bubblenest. If you intend on breeding them let the male tend to his nest and remove the female after shes released her eggs. Im no expert on anabantiods so thats about all i can tell you.
Shae