Any idea of their age? Do they all quack, or do any kind of mumble and whisper? The curly drake feathers show up when they are mature, I believe (I have all girls right now).
They look like crested Pekins to me.
Something to be aware of is that a guideline for drakes to females is one to three. If you only have one boy, you should be in good shape. Otherwise, more duck multiplication may be advisable! But everyone's case is different, so I would not be in a big rush. See how it goes, but be aware sometimes drakes can be overzealous in mating, and more females makes a better, healthier flock.
Congratulations!