I think that Feliway helps keep the peace somewhat in our house, but I don't think it's a miracle drug. It is known as an aid to help with aggression in multi-cat houses, so it's certainly worth a try.
We have two cats that sound like yours - one is always beating up on the other. They've been...
Ugh...I once tasted metronidazole and it was nasty. We have had the best results with Pill Pockets. But, you don't need to use the whole thing...just rip off enough to cover the pill. What we do is give our cat a few empty pieces first and then sneak one in with the pill in it and then give a...
We have had good luck with Feliway spray. I think it works well, but it's not a miracle drug. I'm betting that within a week everything will have settled down whether or not you get Feliway.
But, if you do, the plugin really only covers one room, so I'd put one in just a couple of the rooms...