Can you post a picture of what you have? Their feet do look pretty bad, so I would suggest getting them started on Cattle B Injectable Complex, Durvet Brand, 1ml a day for each duckling until symptoms improve, it can be put over their favorite treat or administer orally with a syringe or...
Adorable! :love
I see in a few pictures their feet are overlapping, are you providing them a niacin supplement or feeding them a feed formulated for duck?.