Not as bad as you'd think. There's some disagreements here and there, but overall they pretty much all get along. The only exception is Jeeves, a black and white cat. For some reason him and two of the others don't get along great, but it's manageable at least.

Just to add to my other comment, It also helps where I live. I have a small old two story house with a basement, so there's 3 levels and lots of little nooks and crannys for them. I have several litter boxes in the basement and on the main floor as well, along with 3 water stations and 4 main food bowls. (Although for wet food and treats I usually have to also break out some dishes so they get a more equal distribution, especially because of Moops (second grey cat down from the top right of the pic) who is very much a food orientated cat, and likes to hoover up as much a he can before anyone else gets a chance.