I agree with keeping them with dwarf cichlids. As a person who has kept both Mesonauta festivus and Mesonauta acora, I don't think I'd choose a festivum as a tank mate. They can be fairly pugnacious as adults (more like angelfish in terms of behavior than keyholes). I think in a larger tank it could work, but I wouldn't try it in a 3' tank. Rainbow cichlids are pretty passive, you might have some luck with one of those, but just given the tank size I'd be more inclined to choose a pair of Apistogramma, rams, possibly Laetacara. Dicrossus are pretty delicate, so probably avoid those, and I think a pair of Pelvicachromis might be kind of rough on keyholes so probably avoid those too. Just my thoughts.