Looks like Lice Nits.
The eggs are basically "glued" to the base of the feathers. Are you seeing actual crawling bugs or lice on the birds?
To help unglue to the Nits, you can apply some coconut oil and they will start to come off. Some people pluck the feathers, but if there's a lot of them, that may not be practical.
Here's a bit more info with photos to help you I.D. whether you are dealing with Lice or Mites. While treatment can be the same, using Permethrin based dusts/sprays, the 2 "bugs" do act differently and have a different life cycle, so knowing what you are treating and how to treat can help you win the battle.
https://the-chicken-chick.com/poultry-lice-and-mites-identification/
https://bitchinchickens.com/2019/09/12/northern-fowl-red-mites/