That would work if you want to feed them the whole bag at once. I buy the biggest bag because it's cheaper so I just use a little at a time. Maybe about 1/2 cup per duck. So I put it in a bowl and run the water on it.
Yes about 1/2 cup. Duckling would get a lot less especially at first, maybe a teaspoon per duckling. Wait until they are four or five days old at least I think.
Ah . . . those aren't very good odds for getting a crested duck.