My experiences: sorry for the novel!
I’ve done this twice now, with good but different results. The key is to introduce them slowly. How slowly depends on the personality of the cat. Allow each of them their own spaces at first (especially important if you are ‘rescuing’ a cat).
First Time: My sister was planning on going to Korea for over a year, so I took care of her cat Alice. Now, when my sister adopted this cat from the humane society it was made clear that she would prefer to be in a one kitty household. However, due to circumstances and the fact that I ended up taking care of Alice for longer than a year, I later moved into a new apartment with a friend who also had a cat.
We kept them separated for well over 3 months. Not optimal, but considering Alice’s personality, it was not surprising. Alice was not easy going around other cats. At first, when she so much as smelled the other cat’s scent she would growl and hiss. What we did was have a home base for each cat: our respective bedrooms. The cats were only allowed out into the main apartment when the other kitty was safely in “her” bedroom with the door shut. It was actually pretty easy to do. My roommates cat was 14 at the time, so mostly slept and ate. Alice really liked to have “her” space and didn’t like to venture out.
So for nearly two months, the cats never saw one another. This timeframe is a lot longer and a lot more drastic than you probably will ever deal with, but it’s how introducing two alpha female cats (one of whom doesn’t like other cats) to one another goes. The basic idea is to separate the cats, each with their own “home base”. Then start bringing in blankets with the other cat’s scent on them. Then let them smell each other under the door. If they’re still growling/hissing at each other on opposite sides of a closed door, they’re not ready for a face to face. Cat’s have a good memory, so you want to be careful to create positive experiences for them.
Once Alice settled down (first she stopped hissing at the smell of the other cat, then she stopped hissing through the door) and in general was more calm, we started opening my bedroom door so Alice could look out into the apartment. We started with small intervals, like 5 minutes. This allowed the cat’s to see each other (occasionally - as the other cat walked through the hallway) - but were never allowed to get close enough to cause each other harm. At no point in time was the other kitty allowed to come into my room - it was Alice’s room only.
Soon Alice was calm enough we kept the door open all the time. Alice still preferred to stay in my room, but would venture out on occasion. The cats were never friends, never would sleep close to one another (or even with 10-15 ft of one another), but they were not aggressive, not territorial, and would not bother one another. (As a side note, we always kept separate litter boxes.) After about 5 months at the new apartment I had to put Alice to sleep so I don’t know how the cats would have reacted with even more time. I think that it would be the same: cool and disinterested, a kind of “If you don’t bother me I won’t bother you.”
Second Time: Much faster, with much better results. A few months after I had to put Alice to sleep I adopted Delia, an 11 month domestic long hair. Delia is really, really calm for a young cat. I kept her in my room to start, following the same routine. She had been at the shelter since she was a kitten, so everything was new to her. After a week and a half, we opened my door. Delia was curious and started venturing out but always had her safe space to run back to when she was scared. At first we locked up the other kitty when Delia came out, but pretty soon we allowed both of the out simultaneously. Now about 10 months have passed since we introduced them to each other, and they’ll sleep on the same bed, or even the same lap. They don’t curl up with one another (the older cat likes her bubble) but if Delia had her way they would. They share the same litter box, even the same food without problems.
So it is really dependent on the personality of the cats. If you’re adopting a cat, it would be extremely rare for you to get a cat who doesn’t like other cats. If you have a cat at home, most shelters won’t allow you to adopt a cat that doesn’t get along with other cats. Most people won’t or don’t want to take 6 months to introduce cats to one another, and I don’t blame them. My situation was a bit of a freak occurance. :lol: But at least it can be done, with time and a lot of patience.
It is generally recommended to get a male if you have a female cat at home. Males are usually less alpha than the females. :lol: But while that’s a recommendation, if both of the cats like other cats, there’s no reason why you can’t have 2 males or 2 females. I’ve never heard that about someone non-family carrying the cat in, honestly I don’t think it matters as long as your very careful to give them equal time and attention.
Also, if you get a kitten, and not just a young cat, I’ve found that cats are usually much more tolerant of the antics of a kitten then they would be of the same behavior coming from an adult cat. But as long as you take the time to slowly acclimate them to one another, you should be fine no matter the age of the cats.