I've read that is is best not to intercede, but rather allow the cats to work out their rank and pecking order on their own terms, even if some fur will be flying. Schuyler and Debra (blk/wht) get into some wicked altercations and it is hard to sit back and watch without interfering, because he has vision only out of one eye and she swats him about 4 times to his one swipe. He is much bigger, but she is much quicker! They go at it for a few rounds, but then all is peaceful once again in catville.

You may want to try spraying Feliway, and I understand it also comes in a plug-in version. The synthetic phermones are supposed to mimic those excreted from the cats' cheeks when they scent-mark, thereby imparting a calm and relaxing atmosphere to them by reducing anxieties. It may help with your situation.