+1 with the rock territories, try having 2 separate rock piles as suggested by smidey at the moment there is 1 structure so the dominant fish are trying to claim it if you split the rock/coral into 2 piles you give the fish more territories to claim.
If you go for 3 fryeri will this be 1m and 2f, not sure this will help as fyeri females are notorious for crossbreeding with peacocks so the 2 female fryeri may cause your male peacocks to start fighting. I would suggest a single male fryeri.
Are you sure it is the yellows that are causing the problems, they are usually pretty mellow i would have thought it would be the dragonbloods or lwanda or lemon jake that would be kicking off?