I wish I could offer some advice, but instead I can just offer my sympathy. We've spent the last year trying to deal with our Tuna/Corkscrew issue. The bloody fights, spray wars, peeing on furniture... The best solution we've come up with is just to keep them sepatated. Tuna and Pocky get their run of the house during the day. Corkscrew and Tibby get their run at night. Sometimes we'll let Pocky interact with Tibby and Corkscrew since there are no problems there and Tuna with Tibby. However generally we just keep them in pairs. It's a pain but it seems to work. We still haven't tried medicating them, but we are open to the idea and might look into it in the future. But for now things seems to be going well and we haven't had spraying or peeing on furniture for a while.