So sorry you lost someone.
Must be fun to keep up with such a range! Right now, all eleven of ours are 2.5 years old.
Wondering if you might set up some kind of interim area for the ducks to noodle around in until everyone has laid, then let them go elsewhere. Just trying to think of ways to keep the eggs in a known territory that can be picked up before the crows arrive.
In our case, crows are our allies. They eat what the cats kill (rodents), and warn us of approaching trouble. I don't doubt they would take advantage of a food opportunity (eggs) if it presented itself, but so far, the relationship is amicable.