Everything everyone is saying sounds right to me. Mine all get along really well though, but I have 5 (recently added 4 green tiger barbs also though so 9 total). When I add new fish they will nip at them for a little then they get bored with that and just chase each other around again. Yours seem a little more violent than mine but like everyone else said, that is just how they are. How big is your tank? If it is small I am sure that will make them fight more.