Multi-Cat Households with Multi Cat Haters?

Wondering if you'd have any advice for a multi-cat household that has multiple cats who are semi cat aggressive?

Bea is approx 6 years old. Began fostering her in Feb, she'll never be adopted likely. She was adopted/returned for not getting along with other kitty in home (people were dumb & tossed the 2 cats together in one room the first night they brought Bea home). She tolerates one "flighty" kitty, but is constantly fighting with Ophelia Rose. Ophelia is NOT nice to other cats, she generally seems to stalk/attack them, especially new cats in "her" house. (FYI - Ophelia is deaf as a stone)

I just wish for remote peace between the two. Tried Feliway diffusers, tried Resuce Remedy, tried both combined, no success. I've done intros/re-intros. Any advice?

Right now, they live in seperate rooms/areas. If they could get along, that would double their living space....and give me some sense of sanity.

Adding this....I've also tried vanilla, switching out bedding, bathing them in the same shampoo at the same time (both cats get regular baths due to one being a not clean white cat & one being a greasy/poor grooming white cat). We've had exams to rule out health issues, etc. Ophelia Rose is on Buspar as she is slightly "unhinged". I have cat trees, lots of windows to climb in....problem is Bea is incapable of climbing. (She was a declaw gone wrong, was re-declawed, and does have mild arthritis) I have been through & cleaned the house thoroughly hoping on some chance it would help.

I have no good suggestions just wanted to say I feel your pain.

I live in one and half rooms with 3 cats that don't get along.

My fourth cat had to go live with my best friend in her bedroom because
he was very aggressive towards humans and cats and since I did not
have the room to segregate him, other than the bathroom, we felt it
best to put him in her bedroom since she lives in a house. he is doing better
now that he has more room and no targets.

I never heard of the vanilla thing ...what is that ?

I have heard that thyroid problems in cats can make them aggressive
so as soon as I get some extra money I am bringing my aggessive
kitty to have his thyroid checked. But I also heard that these are
specialized tests and lots of vets do Not know what tests to ask
for so research should be done before going to the vet so you know
what to tell the vet as far as what tests he needs to order.
Otherwise I think they would just do a general thyroid test.

Anyway.... sorry I was no help.
good luck and keep up the good work !