Stopping fairy wrasse aggression by adding a third.

So this is my second attempt at getting fish additions to my reef tank. I presentry have in my 75gallon display tank a yellow tang, bicolor angel, 2 occelaris clown and a yellow watchman goby. Bought 3 green chromis because liveaquaria said they were peaceful. One killed the other two off. I returned him to lfs and I purchases a salon fairy wrasse and a yellowfin fairy wrasse and the salon is harassing the yellowfin. They are supposed to be peaceful fish. I am either very unlucky, my 37 gallon quarantine tank is set up wrong or there is something I am doing wrong. Years back I resolved aggression between my bicolor angel and marooned clown by adding a third inhabitant damsel. Damsel kept the others in line. Do you think this would work with these fairy wrasses? If so what do you recommend?
Thanks