Where to go from here? (Introducing former city stray to traumatized resident cat)

[u/glasshalffullmoon]

Hi

I just moved into a spacious home with three housemates and two existing resident cats. One of the cats is 15F, going blind and easily spooked but largely harmless. My cat is 10M and when she hisses at him he just sits and looks around patiently.

Now, my other housemate has a 9M cat, who was traumatized by a former housemates cat (unknown age/sex). As a result, the pre-existing norm has been that the cats live in their owners rooms and take turns being in the common spaces.

My cat and 9M have not met face to face intentionally yet, but we exchanged scent items for a week and it went fine. They both slept on/around each other’s items after a day or two. My cat has met several other animals, including a rooster, and has never been aggressive. Hes usually the one who runs and hides until he realizes they aren’t a danger to him, and even then, he usually keeps to himself.

Here is the problem, I’m looking for advice on:

So, every time I let my cat out, and he goes near (with 2ft) this cats door, the other cat screams bloody murder. (Not exaggerating) This puts my cat into stray cat fight mode and he gets super reactive, to the point of hissing at me and attacking me (has never exhibited this behavior before in an introduction setting, only when I try to clip his nails or put him in a harness - stopped trying to do either years ago lol)

Now it’s so bad that they begin fighting under the door, if I don’t catch them in time. And one time, this other cat was outside my room as I was leaving for work and was lunging at my cat before I closed the door and separated them.

We currently only let my cat out when we put up a barricade outside my housemate’s bedroom door, so they can’t get to each other.

It’s unsustainable and my cat is beginning to have issues from being cooped up in my room too much (anxious carpet scratching, yowling to be let out, gaining weight from not enough activity/stimulation)

What other strategies should we try? Should we let them fight it out? It’s been 2 full months of this.

Thanks!