Well since our guineas were older, 8 weeks, and had already been free range before we got them, after a week caged in the coop, we released them. They have done great with our chickens!! Just act like they are all one big flock. The hens of course peck at them on occasion, but they do that to each other also. Guess just reminding them who is boss. They haven't hurt them or anything though. Even all eat from the same feeder. The guineas will not roost in the coop at night however. They stay close and eat with the chickens every day, but disappear at dusk.
I worry they will get eaten, but so far so good.