How much space do you have - coop/run - square foot of each?
How old are your roosters?
How old are your girls?
I agree, a saddle may help her. I would put some BluKote on the scabby skin, let that dry, then put on the saddle.
As
@micstrachan mentioned, you need to know
why there is feather loss/damage. Likely your answer is the 2 roosters. That looks like rooster damage to me.
Personally, I would not separate the pullets/hens, leave them all together.
Separate out 1 or both roosters. You mention that one is particularly nasty - what does that mean? He's nasty to people, to the pullets/hens or both?
Photos of coop/run and flock are always welcome.