What's definitely not normal is for ducks to have hair on their necks... We call it feathers...
I keep only one duck and one drake (Muscovies) and though he chases her around occasionally when she wants nothing to do with it, that's just how duck mating is sometimes and he never causes injury, and she often just flies away for a bit to get a break if really needed and sits on the roof or something. Sometimes it's annoying, but it's his one job, and the eggs have get fertilized somehow, so I don't punish him or hold it against him for doing the job we keep him for.
If the situations not to your liking or proving dysfunctional for all involved, you can separate them and/or find the drakes a new home (or cull and eat them) but please don't punish an animal or blame it for doing what it's supposed to just because it doesn't fit your plans or because you've hitherto failed to manage the situation properly...
Not trying to sound too harsh. Because we're all still learning something. But I just felt that point needed to be emphasized. GL!