Are both ducks male? The drake will continue to mate your hens if you allow them to live in the same run. Male ducks have "equipment" while roosters do not, so a drake and chicken hen have incompatible parts, if you catch my drift. Drakes can injure chickens if they try to mate them.
If your wife isn't too attached to them but still is set on having ducks, you may be able to compromise. You could get rid of the drakes and order two sexed female ducklings from a hatchery online, like Metzer or Meyer. There are lots of hatcheries that sell sexed chicks via mail. If you don't havery the heart to butcher, you can try re homing them, or even try your local shelter. One of the shelters near here will take any kind of farm animals. If she doesn't want to get rid of them, the best option would be to somehow separate them. You could also try adding a few female ducks to your flock and a kiddie pool. Drakes much prefer to mate on water, so if he sees females smashing around, it may take his attention from the hens a bit.
Good luck!
