Desperate for behavioral advice for merging my cats

Okay, long story short, I am trying to merge my 10 year old cat who has never lived with other cats (she lived with my parents) with 4 others cats. My 10 year old cat, Bubbles, was very sick so I kept her away in a separate room while she healed. When she met the other cats she hissed and tried to fight with them, but slowly backed off of doing that and the cats kept their distance... until one day our male cat, 6 yr old (Simon), started fighting her. She is kept in a separate room while they are merging and have definitely had moments where they are in the same room and just sit there. There is obviously hissing, but it eventually fades. Recently, Simon has been bolting into the room and attacking Bubbles. Now Bubbles will not come out of the room and is terrified every time I open the door. It's been roughly 4-5 months and there has been almost zero progress of them merging.

Am I hopeless here? Does anyone have any advice on what I can do to help Simon and Bubbles with the merging? I have tried hormone spray, food through the door and even with it open, allowing them to naturally see each other. I really don't want Bubbles to be locked in this room for forever. I know the goal is not free to have them be best friends but she cannot live here if she's going to be attacked all the time. I need the craziest advice or things that have worked with cats. I will try anything at this point so I don't have to send her back with my parents