There's only 4 in my flock and 2 are ducks. Everyone gets along well but if you observe them you'll see subtle signs to show who's top bird and whose not. I imagine it probably gets more difficult with more birds. My top girl is always first at my feet for treats and blackie (my lowest) is usually a few steps back patiently waiting for her turn. While they are scratching around the yard every once in awhile someone (duck or chicken) will peck her neck to remind her she's lowest its pretty quick and she let's out a quick squawk and moves on- so if you weren't watching you wouldn't notice. And on the rare occasion my big duck will grab her neck and hold her down- which is pretty violent looking so I try to intervien but it only lasts a few seconds so its over by the time I get there. And my girl duck will stand up tall and follow blackie around essentially pushing her back with her chest. Oh and everyone will steal her treats -altho I've seen her steal treats to BUT she usually steals and runs away with it. When they steal from her they just push her out of the way and eat it in front of her. Poor thing! Idk if that helps you figure it out or not.
