PERSONALLY, I do not tolerate bullies in my flock.
First, I check to make sure there isn't a reason for the nastiness. For example, do the girls have PLENTY of room ? ? Does the picked on one have places to hide and get away from the others ? ? ? Are there a couple of feeders and waterers out ? ? ?
You may only need one feeder and one water, BUT if some hen has declared it her territory, then a second feeder / waterer provides a place for the lower place hens to still eat without dealing with the confrontation.
So, you have two girls that are nasty . . . If they were mine, I would get rid of them and get two - three new ones. The two girls may go to a new home with a new batch of hens and find themselves in a whole new pecking order. My EE use to be on the bottom. I got rid of two hens that were always picking on her. I brought in two new pullets - -- a little younger than the rest of the flock. Those two are on the bottom now - - - -but nobody picks on anybody.
I have a good flock now where everyone gets along just great. I have 16 birds together and they are in three different age groups. I believe in bringing in at least three birds at a time. The new ones kinda co-exist with the existing groups. Sometimes, they sleep in different places and hang out with their own groups, but everybody plays nice.