I added two standards to my bantam flock of 4, and the standards let the bantams boss them around! Depends on who was there first, how old they are, and how they're introduced.
Some pecking/drama is to be expected, just watch for blatant aggression or injury. Always give atleast 2 weeks of them seeing each other but not having direct access. You can get an idea then of who might be a problem chicken.
Chipmunk, my D'Anver hen, will pace the cage of new arrivals, fluffed up like she's some kind of chicken cop on patrol. So she's the one who gets locked up on introduction day. After the others play nice, then I let her back out, she does her thing, and everyone settles back in. I have 3 places in my coop where they can seperate themselves.. egg room, roost, above egg room. My standards hid in the egg room for about a week, before finding their place on the roost. And chipmunk shares the roost with them. Took 2 weeks of seperation, and 2 weeks total of integration for my flock.