Sounds like these birds need an antibiotic right away. I don't know 2 cents worth about them. All i know is that these birds need treatment before they all die. When you get everyone back on track, look for the cause. Unless you live in a very warm area, winter's temperature fluctuations and cold are very tough on chickens.
Feathers only go so far to keep a chicken warm, and even ducks can only take so much cold.
Our winter weather has been major screwy - one week biting cold in the negatives, the next, sunny and upper 50's. One good thing is that they're still eating well. Called the vet and now all are on antibiotics. One is now so bad that she can hardly open her eye. On two others, there is a frothy, spit like build up on the eye.