Dwarf cichlids can be pretty nasty. I had a BABY apisto chasing my Blue Ram and Dorsigera around. I had to put her into another tank so the others could get some peace! Don't think I'll be getting any more dwarf cichlids anytime soon.
And wait, you have them in with a red tail shark and barbs? I don't know about odessa barbs, but most barbs are at least semi aggressive, and I could see them having a go with the dwarf cichlid. As for the red tail shark, they get fairly big, and it will quickly outgrow a 30 gallon tank, and if you keep it in there, it could end up killing the other fish. They are naturally aggressive, but being in a small tank on top of it--disaster!