Well, I should've done this in the first place. I google searched yellow cichlids, and up popped Electric Yellow Cichlids, which appear to be what they are. Also, he got them from PetSmart, and I looked at PetSmarts Cichlids online and they sell Electric Yellow. The yellow ones are the ones he's added to the tank. I think all the rest came with it, but there are other things (like Plecostamus, Sharks, Cat Fish, Gold Fish, etc...) that he has added. I think it's way overstocked, but it's not my tank and his fish seem to survive okay.
Is there anyway to sex them?