I have a similar problem. I have one cat, Princess Ivy, who gets picked on by pretty much all the others! I have one room in the house, my computer room, that is off limits to all the other cats. Only Ivy is allowed in there. She has a litterbox, toys, scratching post ect in there. She spends a couple hours a day on her own. It greatly reduces the tension between all of them!

Since Harry is the instigator in your house, is there some way you could isolate him for brief periods? Like a kitty time out!

I use the Feliway diffusers too. I have three of them so most of the house is covered. I think they do work. I can always tell when they need to be refilled! I think they reduce the fighting, as well as helping with peeing in the wrong spots(like the kitchen counter!). I buy them from entirelypets.com. Even with the exchange rate and shipping, it costs about half of what my vet charges for them.

I put Rescue Remedy in the cats' water too. Don't know if it helps, but it can't hurt.