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Most if not all egg laying cichlids will defend their nest/cave area from other fish. One way to cut down on the chances of the other fish getting hurt is to have a large enough tank with breaks in the line of sight.
So yes once a pair of convicts breed chances are the others will end up hurt or dead unless they are housed in a large enough tank with lots of cover . I have a pair of Thorichthys sp. "Gold Mixteco" that are about 4-6" and they will rule a whole 55.
I'd consider only putting 2 they will pair. They will reek havoc on your other fish.
I had 2 pairs and the spawned at the same time on separate parts of my tank.
They killed my 6 inch oscar... And had everyone else at the surface to avoid their protection efforts.