Since you already have aulonocara or peacock cichids I would just stay with them. Do not ad any Mbuna to that tank as they will beat up your peacocks, and haps will get to big. You can get haps only if you plan on upgrading to a bigger tank in the future.
You sould probably only add 1 maybe to more fish to that tank. 30gl's is pretty small and most pecocks get to around 5in. The fish you add try and make sure you get a type that has a different color than the ones you already have or just try and get females or males of the same type of fish you already have. Just try and keep one male to a tank though.