Hi there! I actually work at a cat cafe, so I feel qualified enough to answer this question lol…
It sounds like you’re already on the right track! Having the kitty acclimate in their own separate room will alleviate a lot of stress for the both of them. The resident cat and the new kitty will be able to smell each other through the door. For the first little while, we want their only interactions to be through the door WITHOUT seeing each other. For an added extra boost, you can start feeding them at the door so that they associate food with the other cat’s scent.
Once they seem used to their scents you can start cracking the door and gauging their responses to seeing the other cat’s face. Expect hissing or growling, this is normal. We want to continue associating the other cat with something good, like treats! Crack the door for a split second so they can see each other, then close it and give both cats a treat. Do this several times a day. Slowly you can begin keeping the door open for longer periods of time, but close it if the cats get too aggressive. The best case scenario is that they begin to not react negatively to the other cat’s presence and they start to tolerate each other.
At some point, if they stop reacting negatively, you can give them supervised time together in the room. Make sure to feed them plenty of treats and play with them to make it the least amount of tense as possible. Every cat is different, and will take different amount of times to become used to other cats.
Since your resident cat is already 8 years old, it is unlikely that they will be all cuddly with each other at least for a WHILE. Be prepared to deal with any dominance battles, particularly if the resident cat has been an only cat all this time.
Cats can be super stubborn, so it’s important to remain patient!! If you have any other questions I would love to answer them, and I wish you the best of luck. Give both your cats lots of love for me!! 🫶
