You can easily have 2 convict cichlids in a 30 gallon tank. I've had them in 20s with no problems. I have never seen a convict with "monster" behavior, but you may get lucky. Those feeders may die, but probably won't get eaten unless they are feeder guppies/danios/white clouds, or if they are very small goldfish. They may get killed if they are larger, but why waste them like that?