Check the label on your feed bag for milling date and percentage of protein and possible mould (strange smell?)
Where exactly are you storing the feed and how much do your chickens and ducks eat every day?
They need about 110-130 grams of feed per bird per day depending on breed, age and body...
The two new ducks, are they in the same coop and run with the hens?
If so, they will be seen as intruders and prevent your hens from starting to lay for quite some time (a few more weeks).
Are your ducks both females?