All i know is with that much live rock and those 3 tangs, its gonna be hard to add anything else, have you though about trying to remove the mean ones (place them in the sump for a few days/ a week long) and then add the new ones and let them get established. Your tank right now has enough space to add a few fish, though i dont think more tangs are the best idea unless you plan on upgrading in the future 12-24 months... to a much larger tank. all of those fish get 8 inches+. And seeing as how you already have 2 zebrasoma tangs, that in itself could cause a problem down the road as they get larger...