Introducing a new cat to the family and having issues. Any help is welcome.

I’m new to the sub, so please go easy on me.

I’ve got a male cat (M), 3 years old, and a female cat (F)1.5 year old. When I brought in the female cat originally, M wanted nothing to do with her. He likes to escape the house a lot and get outside anytime someone opens the door, and can be quite a rascal. F is the sweetest baby in the entire world, and is always trying to play with M, but he either ignores or hisses at her. She rarely gets to play with anyone but they do chase each other around the house at times and play. It’s been over a year and it’s still like this.

At this point I’m thinking ok, maybe if I get another kitten, F will have someone to play with and a cat who is sweet like her.

So my sister in law has a sweet baby boy (We’ll call him L) who somehow survived a ride in the engine block of a car for 6 hours until they found him. He’s the sweetest most loving cat, and they needed someone to take him. I thought, this is perfect…

I bring L home, get him a room to himself and he stays in there for 3-4 days, we give him food and water and toys and let the other cats sniff the door and stuff.

I’m using pheromone diffusers and sprays, and after about 4 days I gently try to introduce L to F.

She absolutely fucking HATES it.

Like she hunkers down and starts growling and hissing and I have never seen her like this. L was sweet and gently backed away and didn’t try to press it. Gave it a couple more days, tried again, same thing.

At this point I’m worried because I want to keep and care and love for this baby, but I absolutely don’t want to make life stressful for F, who I was trying to get a playmate for.

Maybe I missed a step, hopefully someone here has some advice on this because I’m starting to feel a bit hopeless