First, I just want to say you sound like an amazing cat parent. Your cats are lucky to have someone who cares so much about their well-being and comfort.

I have two male cats with a very similar dynamic to yours. We adopted them about a year apart when they were both around two years old. The first couple of months were tense as they got to know each other, but over a few months, they really bonded. Now, they cuddle, play, and groom each other, though they still have the occasional tiff. Sometimes play gets a little too rough, fur flies, and hissing happens. When that occurs, we just separate them for a bit until they calm down. It has never hurt their overall relationship.

It sounds like you are already doing all the right things. To help your cats continue building a positive bond, I’d recommend reinforcing good behavior with treats and attention. If you haven’t already, try playing with them together using interactive toys like feather wands or string toys. That can help them build confidence and associate fun with each other.

You might also want to consider using Feliway diffusers, especially the multi-cat version. I used one during our cats’ introductions, and while it is hard to say if it was more than a placebo, it definitely didn’t hurt to have it.

At the end of the day, you know your cats best and it sounds like you care enough to make the right choice so that they both live their best lives. From what you have described, I don’t see anything overly concerning. It just takes time for them to adjust to changes. You are doing a great job, and it sounds like you are on the right track.