There are several things you can do. First, make sure that your hens have plenty of coop/run room so that they are not overcrowded. Your coop should have a minimum of 4 sq. ft. of floor area per bird (not counting the area taken up by the nest boxes) and 10 sq. ft. of floor area per bird on the run. Overcrowding can quickly lead to the kind of behaviour you are describing. Put some Blue Kote Wound Dressing on the areas where your hens feathers have been pulled out. Not only will the Blue Kote protect the bare skin and promote healing, but the bad taste of the Blue Kote will discourage other hens from pecking at the areas. If you're not familiar with Blue Kote Wound Dressing you can see it at
https://www.mcmurrayhatchery.com/blue_kote_wound_dressing.html. If having done all these things, you are still having problems with the two bullies, you can put some pinless peepers on them. The pinless peepers will prevent them from being able to see straight in front of themselves to peck at the other hens, yet will still allow them to use their peripheral vision to eat and drink. If you're not familiar with pinless peepers, you can see them at
https://www.mcmurrayhatchery.com/pinless_peepers.html. Good luck in putting a stop to the bullying.