You might need to come to the acceptance that you should not keep all of your chickens. They will not live forever, just like any pet. With a flock, you have to consider is your flock happy and content. They are not happy if they are living in fear, being preyed upon, or beaten up. Even the hens that are not getting picked on, are distressed and upset, and nervous. Even though it is hard to get rid of, or give away something that you are attached too, it is better than your flock to living in unrest for months. From your description, that is where your flock is now.
Sometimes flocks can sort this out, but more often, as often reported on these boards, the pair will fight until torn and bloody, or one is dead, and the other is torn and bloody. We all wish that they would all just get along. And we tend to think the mean ones are evil, but it is important to remember that they are chickens and see survival from a chicken stand point, not a human one.
As stated up above, you will need to get more pens, and that will be expensive.
If you just have a small flock, and are not into a breeding program, I would highly recommend only one or possibly two roosters, knowing that it might take several tries with different roosters, till you can find two that will work together, if you have your heart set on having roosters. Or even just having hens without roosters. Chickens need to be part of a flock, the flock will have its own dynamics, sometimes you have to adjust the flock to achieve that, but a successful happy flock is worth it.
Mrs.K