I would let them free range together all the time. It is the best way to get different chickens to accept one another. They have the luxury of doing it in their own way and in their own time. Because they are outside, they can easily run away from each other when someone attempts to become aggressive or territorial. So I would recommend always free ranging with all the girls together. Over time, they will come to unite into one flock who sleeps in separate quarters. I don't know think it really matters which breed you add to the existing flock. Which ever 3 go over, there will be issues with pecking order establishment and that can be very hard. For starters though, let everyone free range together as much and often as possible.