They all look like pullets to me right now, though it is still young to tell for sure with the Silkie. Your Blue Orpington is indeed a Blue Orpington, but it is of the black variety. Mated together, blue birds produce true blue, black (like yours), and splash colored offspring.
Whew! I feel relieved that so far, they look like hens. The barred rock and golden laced wyandotte go at each other a lot and often assert themselves with the others. But when either of them 'start in' on the mottled cochin bantam....wow...look out. She comes back at them full force and they leave her alone for a while. She is still the smallest in the brooder....but mighty for her size. I keep an eye on her to make sure she isn't hurt after the encounters.