It seems like you have enough run space that you could temporarily close up the run and not allow any free ranging until the cockerels learn to stand up to the two bully hens. Assuming the run part is predator proof, the cockerels would be safe overnight on nights that they can’t get past the hens. Eventually the group dynamics will work themselves out. Especially with breeding season right around the corner. It won’t hurt them to be confined for a month or two.
My second choice that I would try would be to isolate the Beast in a wire dog crate for a few days. That should knock her down a peg or two in the pecking order, and hopefully when she is reintroduced she will be less of a bully. Since her sister is ready to step into her bully shoes, you might have to separate her into another dog crate as well. When it’s time, I would reintroduce them separately. One first and then a few days later the other. (If you isolate them together in the same crate or pen, then when they get back to the main flock, they are still the same bully two pack that they used to be.)
That is a lot of work, managing two different dog crates for a week or so, and moving birds around and monitoring each move’s effect, which is why I personally would just try my first idea instead.
As I type, a 3rd option comes to mind. It looks like you have enough room that you could scan Craigslist (or FB poultry groups) and buy a handful of mature adult hens, ideally from the same place. Throw them in and see if they don’t push the Beast out of top position. Then in the spring or summer when you are ready to integrate your juvenile chicks, resell any extra hens you don’t want on Craigslist.
Actually as I think about it, any option that involves buying more chickens (
) would be at the top of my list! 
My second choice that I would try would be to isolate the Beast in a wire dog crate for a few days. That should knock her down a peg or two in the pecking order, and hopefully when she is reintroduced she will be less of a bully. Since her sister is ready to step into her bully shoes, you might have to separate her into another dog crate as well. When it’s time, I would reintroduce them separately. One first and then a few days later the other. (If you isolate them together in the same crate or pen, then when they get back to the main flock, they are still the same bully two pack that they used to be.)
That is a lot of work, managing two different dog crates for a week or so, and moving birds around and monitoring each move’s effect, which is why I personally would just try my first idea instead.
As I type, a 3rd option comes to mind. It looks like you have enough room that you could scan Craigslist (or FB poultry groups) and buy a handful of mature adult hens, ideally from the same place. Throw them in and see if they don’t push the Beast out of top position. Then in the spring or summer when you are ready to integrate your juvenile chicks, resell any extra hens you don’t want on Craigslist.
Actually as I think about it, any option that involves buying more chickens (
) would be at the top of my list! 
