HI VICTORG, WELCOME TO FISHLORE!
I'm sorry your post got so far down on the list, and no one answered.....I'll give a shot at it, and maybe someone else will chime in...
If you post in the cichlid section, more people who know about these fish will see it....
I would say the tank you have is bare minimum....if they had a larger tank, it might help the aggression. ALSO it has a lot to do with the tank decor . Are there lots of rocks and caves, driftwood and plants that allow for broken line of sight?
I wouldn't add more fish, unless you feel you DO have two males...maybe take one back and try for a female....These fish are suppose to be able to be in a tank with other fish, so you might TRY a different species to give them something else to think about, but only if you are able to get a bigger tank.
Good Luck, and tell us more about your tank....and fish interests...can you post some pictures?