keep in mind they will get big. any of those haps get quite large-i have a nimbochromis venustus and he is 9 inches long (and in a 90 gallon by himself)-the livingstonii will get as large, if not bigger. also, it will eat anything it can cram in its mouth. the only other thing compatible would be other haps-and your tank is way too small for haps. you wont be able to keep loaches or any other small fish in there-keep in mind they are predators and in the wild feed off of other fish. dont be surprised if you put other fish in there and they get eaten.
like mike suggested, get rid of the livingstonii's and get something that will work in there-peacocks, lake tang fish, or dwarf african species would work.. best of luck to ya and let us know whatcha decide!