A little over a year ago, my girlfriend and I moved in together. To our new apartment, I brought my two cats (Cerridwen and Liam, ages 3 and 2) and she brought her cat (Willow, age 6, we think). We knew going in that the cats would take some time to get used to each other. We kept them separated by the bedroom door (Willow in the bedroom, Cerridwen and Liam in the living room) for the first couple of days, then started having short, supervised visits. After a couple of weeks, we started giving them all the run of the apartment, just separating them when we weren't home. After several more weeks of that, we finally started leaving them all together all the time. We had been making a lot of progress.
They weren't friends or anything, but we could see regular improvement. Willow stopped hiding under the bed all the time, and no longer runs every time Liam comes anywhere near her. They mostly ignore each other most of the time. However, we seem to have hit a wall. We got to the point of not needing to keep them separated all the time, and that's where the progress ended.
More than a year after moving in together, there's still a lot of growling and hissing. Cerridwen likes to sleep on the bed with us, and will sit in the middle of the bed and guard it, not letting Willow up. She'll tolerate Liam sharing most of the time, but she'll chase Willow off the bed if she tries to join us. She occasionally will charge at Willow, hissing and spitting, and then stop short as soon as Willow retreats and just walk away. Liam will sneak up on Willow and pounce on her and grab her scruff with his teeth. He just sits on her and holds her like that while she yowls until one of us rescues her. Cerridwen will also sit in the hallway between the living room and the bathroom and refuse to let Willow pass to get to the food or litterbox. Neither of them is physically injuring Willow, but obviously, we need to find a way to get them to accept her.
So far, we've got two Feliway diffusers plugged in, we've increased the number of litterboxes and food dishes so the Cerridwen can't possibly guard them all and Willow will have access to at least one at all times, and we've got water bottles and guns all over the apartment for squirting them when they act like little bastards. When Liam gets really, really obnoxious and refuses to leave the other cats alone (he also seems entirely unable to recognize when Cerridwen isn't interested in playing), we'll put him in Kitty Time Out in the bathroom for a few minutes if only to give the rest of the household a break. We also have Cerridwen and Liam wearing SoftPaws so they at least are hindered in doing too much real damage if there's ever a full-out fight.
Cerridwen and Liam were both speutered at about 6 months old. Willow has been spayed for several years, but did have a litter before she was spayed. I think a large part of the problem is that Cerridwen and Liam were both born in a feral colony (trapped and adopted when they were each about 4-5 months old), and the resident tomcat of the colony looks very much like a purebred Maine Coon. Both of them have something very close to the classic Maine Coon look, and are *big*. Cerridwen is the heftier of the two, weighing in at about 18 lbs of solid muscle. Liam is a year younger, about 13 lbs, and seems to be still growing. He's only really lost his kitten look in the last few months. Willow, on the other hand, is an older, much smaller, 8 lb calico. I think a large part of the problem is that Cerridwen and Liam play really rough together. When they get going, they wrestle around on the floor, biting and kicking, and chase each other all over the apartment. I'm pretty sure that Liam, at least, isn't actually attacking Willow so much as trying to force her to play with him, and she's not having it. Willow is much more sedate. She just wants to lay in a lap and get petted. When they do get obnoxious with her, she won't fight back. She just runs or else sits still and yells for help until she gets rescued.
What are we doing wrong? We can't just let them go on beating up on Willow forever, but I'm out of ideas for ways to get them to stop. I've wondered whether the solution is to just ignore it and let them all fight it out and work out their pecking order, but my girlfriend is already really upset about her cat being bullied, and with the size difference, she's sure to be very much on the losing end of any real fighting. Are we doing something we shouldn't? Does Liam need to be on some sort of kitty anti-psychotics? I know they're probably all feeling a bit cramped with two people and three cats in a 900 sq ft apartment, but it's going to be several months at least until we can buy a house and move. What should we do?