I'm guessing you have a mix of mbuna and peacocks which is probably the main issue. If you can list the specific species we can better help, or if you aren't sure then post pics of them.
African cichlids are also very territorial which is why it's good to rearrange the rocks and introduce new fish in the dark. Some people even remove all existing fish into a bucket, perform a water change, rearrange all decorations, then add the new fish and existing fish with lights off. This puts all fish into a "new" tank at the same time with no established territories.
Finally, a lot of people overstock their tanks so aggression is spread out and no one or two fish is the sole target of aggression.
Sorry to ramble! If you add your stock list we ca give better advice!