Guineas should NOT be kept with even the most stubborn roosters when it's breeding time. They are so aggressive that they'll often kill chickens. Maybe a Goliath rooster (Jersey giant, select Brahma) would put him in his place, but any hens would be easy pickings.
I have 5 guineas and a dozen or so chickens. One coop.
Some Guineas will bully chickens all the time if confined. Mine range freely most of the year, (4 guardian dogs) no problems then.
But In the winter when they can not get out when it is to cold and snow to deep, they do intimidate the chickens when bored. I try to scatter alfalfa hay and give things to peck at and scratch thru to keep them occupied. They still demand to have the highest rung on the roost ladder at night and only tolerate my rooster up there with them. He is a barred rock mix breed, and he just ignores them and refused to get to excited with their antics, he does not fight with them. Another words, he is no fun.
I wish someday to have a sepatate coop for my guineas as i know things would be more peacefull for the chickens.
I love my guineas!
I have had guineas with my chickens for 12 years and never had any injuries or blood drawn by guineas. They dodge at and intimidate but thats it.
If they was a bloddy fight i would see if my pinless peppers would fit on a guinea. Never tried it.