Oh, if they are all males he will be making do with what's about! I don't think ducks are very fussy about that sort of thing. One of mine used to try to mate with my chickens and also my shoe!
Be careful about adding any females because then the drakes will get jealous and will start fighting with each other. If you don't want eggs or ducklings then just keep them as they are and after time they will calm down and the mating behaviour will reduce a lot.
Have you got any photos of your ducks? I as very sad to have to re home my last 3 because they were getting eaten (one a week) by a python in the night. Now I just have my chickens (I can lock they in their coop at night). The ducks would not settle in the coop, and would swim to a small island on our pond out of reach of me!