As long as the smaller species are the breeders and the larger fish aren't being bread you might be fine. Just have dithers, lots of hiding spots of all different sizes, and you should be ok if you raise them together. I honestly would leave the TSN(Large catfish) out. It will end up eating your smaller cichlids.
That won't help at all. I've seen a pair of 3" convicts terrorizing two 7" Oscars.