Dahlia, my brother's cat, and Ginger, my cat, have been getting along better nowadays. When she was very young, Ginger hated other cats. We never had other cats in the house unless necessity forced us to. (Usually in the almost yearly case of a starving or sick cat showing up to the kitchen doorstep. Somehow, the neighborhood cats seem to know that this is a good place to crash for a few months or so.) But Ginger is 10 now, and she's more mellow.
When we first got Dahlia during the last of the three giant snowstorms we had during the winter, we kept her locked in my brother's room to keep Ginger from attacking her. She has free rein of the house now, but I still don't let her in my room. That's Ginger's inner sanctum, and she'd flip if she saw Dahlia in Her sunny windowsill, or on top of Her warm TV, or, God forbid, on Her long-held, never-given up* spot at the foot of my bed.
Ginger still wants Dahlia to give her space though. Even when they sleep near each other, like today, they must have space.Ginger sits on the dining room windowsill and Dahlia gets the floor**, about three feet away. But even then, They don't seem to mind sharing each other's food bowls***, though during feeding time, I think Ginger gets a little jealous If I don't feed her first. Usually when I feed her, she has me sit near her and pet her, but If I feed her second, she'll nip at me and growl till I leave. Weird.
*I was going to Rick-Roll you, but I didn't have the heart. But in the same vein: THIS, which is better.
**I've noticed that they, by some mysterious instinct, seem to know when to move to a different part of the house to follow the sun.I've seen them leave the dining room and beg to be let out to the enclosed porch in the late afternoon, to catch the last drops of sun from the west-facing window.
***Behind each other's backs. They're both too lazy to go up or down a floor to get water or to each any leftover bits from when I feed them in the morning, so they eat from whoever's bowl is on the same floor as they are.