If I understand FIP is a nasty thing for a cat. He - Vicious - sounds like an asswhole. He's 6? Can you put him outside?
Good golly, you must be a lot more tolerent than I am. He'd be begging at the back door and lucky at that.
My cats tolerate one another if not snuggle - the fighters get grabbed and thrown outside. "Go get F**ked! Assholes!"
Now and then, there's a hissy spat but nothing that won't get resolved. Oh, I'm talking Becky's place where there's 5 kitties and I spend most of my time there.

When I had a cat that peed on things, this is what I did:

1) Never leave anything accessible. No more throw rugs. Pull up the bathroom mat everytime you're done. Don't leave anything on the floor, not even shoes if you can help it. If it's on the floor it's considered open for debate.
2) Get plastic tarp to put down on beds, etc until you can get a handle on what is going on with Vicious. This will save you peace of mind. You won't need to change the bedding and the flip the mattress everytime he decides to pee on your bed. All you need to do is wipe up the plastic when he pees. And remember to occasionally change out the tarp because kitty claws might leave some pin holes eventually that the pee can leak through.
3) DO NOT respond to the peeing. This is really important. He wants attention and even yelling is negative attention. DON'T RESPOND. If you do, make sure it's really positive. "Ah, gee, Vicious. You must not have been feeling well today. Well, that's okay. We'll just clean this up and figure it out later." You don't want it to be a contest of wills. So, nothing but a positive voice.
4) Have him checked out for everything. He's approaching old age anyway. My cat quit peeing once we discovered he was diabetic and got his blood sugar under control.

Hee hee - yep, cats have a much different mentality to being 'trained" than dogs do. Cats will do what instinct tells them, and what previous experience has told them will lead to food or petting :) Dogs will simply do something naturally as soon as they have been made to do it several times - hence the "pavolv's dog" experiment. Creatures of habit.

So when you think of it that way, a cat will do what comes most naturally to them - that is, pee where it already smells like pee, because that must be the "pee place". When they're ill, they find something that smells the most like their caregiver and either lay on it, pee on it, or do something to get your attention through the place where you must spend the most time (usually a bed, or clothing that smells most like you like a jacket or pair of shoes).

I know a lot of people have cats that they think are just assholes sometimes, but in reality they are just acting out of instinct."That moved, I must kill it" said Fluffy to the Laboutin shoe. "This smells like me, I'm going to sleep on it" said Muffy to the cashmere coat. "I've peed here before. I'm not a messy cat, so I will continue to pee here because it is the place where pee goes, according to this smell" said Button to the mattress.

If your cat is a psycho, he probably just wants to chase and kill, because he is genetically programmed to do so. Get him a wind up mouse, a scratching post, and some cat nip. Pet him when he's still, and when he wants to run, let him go at it. Put on an oven mitt and play "get the thing" with him. My boy cat Solly used to leap on my back with all claws out when he was about 2 until he was about 4. He was an adolescent cat and wanted to be outside hunting. Since he's an indoor kitty, I got some toys and played "get the thing' with him until he realized that moving, fuzzy thyings that were smaller than him were for killing, and people were for petting. Of course, that logic backfired when we got a little sister for him.. :)