Sometimes there's a hormone imbalance that causes hens to develop roo-ish looks and behavior. I'm not a expert on this, so I'll be learning right along with you :p
Yeah. I'm going by comb and sometimes posture. They seem a bit young right now, so I would hold out for longer. Sometimes they pull the ol-switcharoo. It seems pretty amazing to get that many cockerels.
It looks like a cockerel to me, but it's somewhat harder to sex orpingtons. It's probably best to wait it out. I would cry if I had to give a lavender orp away :hit
Then I'd imagine they'd be digested when they pass through, as long as they got grit. So it looks like worms to me.
Treat all the birds just in case, and I think it'd be fine to eat their eggs when they start laying. I get rid of the eggs for a month when they're being treating for worms, just...
I'm not a expert with ducks, but you're always running the risk of disease when introducing new flock members. Keep her alone for a while to watch for diseases.