Fights for territory reach across many species of animals, including those in the wild, and also, including people. Cats are not exempt from fighting for territory and feral cats brought into an enclosed space may exhibit several territorial behaviors including:
-marking by going outside the litter box
-marking by clawing or otherwise damaging items that smell like other animals
-picking fights with pets already in the home
But don't worry, there are many things you can do to help ease these territorial disputes between your feline friends. One of the things that will help you determine how to go about solving these problems is being a detailed Observer within the first few months of introducing your feral cat to your home.
If there are litter box issues, one of the ways to solve that is by getting more litter boxes. This is an instance where you want to follow the rule of one litter box per cat plus an extra. Another thing about litter boxes is that they need to not all be in the same contain area.
If any of your cats have claimed a specific area as their territory, of course, having multiple litter boxes contains to that area will make that a hostile territory for your other cats, which will lead to them not using litter boxes within the territory of other cats.
This same logic May apply to any scratching post oh, cat beds, cat houses, cat perches, food bowls, watering bowls, or cat toys. Despite the fact that we as humans have been brainwashed into believing that sharing is caring, cats really do not believe this same thing, especially not when you're more established cat feel that a newcomer is encroaching on their territory.