First get those ammonia levels down. you might have to many fish! then I would put in some blue hermit crabs and turbo snails and then a lawnmower blenny!
If you place some more aggresive corals around the xenias, The aggresive corals will sting it and keep it contained to one area!
I have a torch coral near my xenia!
Royal grammas are very terratorial fish and will be aggressive towards any fish. I have not heard of putting more than one in a tank because they will fight each other, but I am not sure of that with a tank of your size!
I can really confirm matti's statement! I had a carpet anenome climb into a powerhead of mine one day and got chewed up and made the tank cloudy with its guts . It did release toxins killing all my fish except for my percs! Ever since I have not had oen in my tank!