You will get mixed results here too
Depending on the sex of the fish you already have, which you don't know, and their "personalities" (which can change when new fish are added), that tank population may be stable OR it may not be. Given that all these fish can get large and breed like mad, you may be looking at a population explosion. Can you give us a pic of your tank, or tell us about the decor and how long you have had the current fish?
On another note, if you are really interested in convicts, would you want to do a species only tank and ask the LFS
if they will take the other fish in trade? I don't advocate swapping out fish, but I'm just throwing out ideas.
One last thought...fish keeping is a life time hobby. There is time for convicts in the future when anther tank is set up or when your current fish are not with you.