They are very nice to each other, i dont think ill have problems
midas cichlids form monogamous pairs. they do this by eliminating other fish, including conspecifics (other midas cichlids) in the area they perceive as their territory. eliminating is a rough process and the result will be shredded or at worst dead fish, leaving only the pair remaining. in a 55 gallon tank, you can be absolutely certain this will happen. same for a 75. in a 120, there "may" be a subdominant male left over.
do yourself and the fish a big favor and when pairing begins, REMOVE the unpaired fish. instead, add 3-4 "target fish". look it up on google.
there were like 20 in a ten gallon petsmart.
almost all LFS's keep such fish in a VERY overcrowded condition. they expect that they'll move the fish out to your house in less time than it will take for the fish to kill each other or die from the stress. it's not a signal that the fish can or should be ok at your house if kept crowded like that.
fish maintained in tanks which are too small or in conditions which are too crowded, develop severe stress syndrome. these fish do not exhibit proper color, do not develop proper fin form, do not exhibit proper metabolic development, do not exhibit normal behaviour, do not develop proper musculature, do not develop properly functioning organ systems and as a result, slowly lose their inherant resistance to disease. this results in a significantly shortened lifespan and along the way, lots of diseases for which the poorly conditioned fish is a good target.