You have been given some great advice. This isn't going to be an easy task. Can you add to your existing coop? Many years ago when I was introducing some pullets to some older hens, one hen in particular would beat up the pullets if she had the chance. I put the bully in jail for awhile a couple of times but when I put her back in with the flock she would start beating up on the pullets again. A few times when she beating up on a pullet I had a fire hose nozzle on the hose, and squirted her with a nice blast of water. She was so intent on beating up the pullet that I really surprised her but didn't completely stop her. She would run into the coop. I eventually cut a second pop door into their coop because she would guard the pop door and not let the pullets go in to eat. She couldn't guard both doors and I put another hanging feeder in the covered part of their run. I finally took her to an auction with some males. Some transition fine and others not so well. I have several coops but back then I didn't. I did get a second coop. Even though the birds could go into either coop, usually the pullets would go into one coop and the hens would go into the other. Now I have the luxury of moving birds to different coops so when I'm integrating I can clean out a coop and blend two flocks into one and very few problems because the coop will be new/different to all of the birds I put into it. They still have to establish their pecking order but it usually goes pretty good. If I have an unusual more aggressive bird, I can move her to another coop with other birds then it's one against the flock but usually goes pretty well. Good luck...