I hear at least one drake (boy) in there, and several females. I would say no less than two of them are hens. You can tell the girls because they have that louder, honkier quack while the males have the quieter raspier peeping still. Beautiful ducks!!
It's hard to distinguish when they're all at it though, especially as the girls can drown the boys out so that may be why they all sounded girly to me. Get another vid in a week or so and we'll probably be able to tell for sure.