what should we do about our cat?

It definitely has to do with your cat…he’s marking his territory.

Are the cats neutered? That may stop the spraying behaviour, but it’s not guaranteed.

There are products you can get at the pet store to discourage cat spray.

he does but I cant let him sleep in my room with me because it started with him having a problem with pooping on my floor. then I put a litter box in there just for him and now he thinks its fun to play in it and scratch in it until he gets all the litter on the floor and he keeps me awake at night.

its just a dominance thing. you should try sitting down (watching tv…etc) with your sister, and have you hold your cat, and your sister hold her cat and pat them etc so they can see that they are both loved equally. cats are not dumb. your cat will get upset when you pat your sisters cat and vice versa. make sure your cat has a place to go (your room would be best) where he has his own spot with his blanket or whatever he has and his toys, where they other cats wont go. just so your cat dosent feel unloved and run away. he needs his own little space.