I have 1 drake and 2 ducks. I found some other duck eggs on craigslist and I was wondering that If I put them in with my ducks if they would sit on them.
Have your females shown any signs of being broody? Do they make nests for their own eggs? If so I'd say try it, and if not, maybe.
Mound up a bunch of shavings into a big nest in the corner of the coop (or in the nest boxes if you have them), and lay all the eggs out in a circle together on top. If your females have broody instincts they will sit.