I introduced two kittens to a house that already has three cats. Yes, I know … that’s a lot of cats but the kittens were born under a bush in my front yard. I fostered them with mama cat and three siblings from birth and found homes for all - two of them with me.
All my cats get along well.
First and foremost: don’t rush it!!! Take long enough that your cat and kitten absolutely want to find out who is on the other side of that door. I’m not talking a day or two.
Second: Don’t give up if you hit a problem. I had absolutely no intention of getting rid of anyone. Start with that in your mind.
So advice:
When you leave the kitten’s room, rub goodbye with a cloth and then rub your older cat with the same cloth to say hello. Repeat when going from older cat to kitten.
When FINALLY introducing the kitten to the older cat - in short segments - multiple times - do so with treats for all. Older cat needs to associate the kitten with happiness. I used treats, favorite toys, brushing one than the other.
Let the kitten explore the house while you pet older cat. Older cat needs to know you love it best.
Let the older cat observe the kitten playing. One problem will be the energy level between older cat and kitten. Kitten won’t understand that older cat may not want to tussle and chase.
Again, don’t rush it. Continue to separate whenever you’re not going to be around - nights or just out of the house - way longer than necessary. Better safe than sorry should be the motto.
Remember that hissing and a swat or two across the face is normal at first. Growling and attack mode are what you need to watch for. Of my three older cats, one hissed at the kittens for weeks. I’d ask her if it was really necessary; she never answered, just continued to make her displeasure known. And then one day, she accepted her “new normal” and gets along with all.
You may or may not end up with best-friend cats. It’s been interesting to watch my cats, old and new, interact. My nine-year old male cat adores the male kitten and vice versa. The others all get along but aren’t besties. They do eat together, sleep near each other, play on occasion, and sometimes take a moment to lick a housemate. I couldn’t be happier.
Make the goal tolerance. Consider anything more lagniappe.
(I meant to add this is the second time in the last five years I’ve done this. Toby is eight. Almost three years ago, my husband and I adopted two kittens from the SPCA. Those three also spent much time apart before getting together but all went well from the start. The kittens - born in my front yard - are now eight months. I just repeated what worked the first time.)