I'm not entirely sure if they still have feathers coming in as I thought they were both done until they molted again. However I could be wrong my first time owning ducks so I'm learning as I go!
This is where I'm focused. It gets blurry, but those feathers look like they're still filling out. I would also check for mites. But barring that... I personally think they just need to grow into them! My opinion only. Do they have a place to bathe and flap their wings?