Most domestic ducks don't fair well if released onto open water, hawks and snapping turtles are 2 predators that will pick them off Owls at night. Also many other predators will swim or just wait until they come ashore to get them. You'd be better off rehoming and hopefully who ever takes them...
Well you could go get them females at least 3-4 each?
That was awful if she knew she was selling you drakes. But drakes can live together with out females they are very handsome boys