I would not use the DE since it will not get rid of leg mites, and it can irritate eyes and breathing of you and the chickens. Oiling the feet and legs 1-2 times a week can treat leg mites. Ivermectin pour-on will treat leg mites, mites and lice in chickens. Dosage is 0.1 ml for every 2 pounds of weight given on the back of the neck, and repeated in 14 days.
Gout may be a possibility. In pictures I have seen, the feet and toes have a lumpy swollen appearance. Some people have had some relief of pain with tart cherry extract capsules daily. Post 1 in the thread below has some good pictures of probable articular gout:
https://www.backyardchickens.com/threads/gout-bumblefoot-or-treatment-see-photos.1064722/
Here is a good article of causes of gout:
https://www.thepoultrysite.com/articles/gout-management-in-poultry
Here is dosage of sour cherry extract capsules from one user in post 15:
https://www.backyardchickens.com/threads/gout-tart-cherry-dose.1319843/page-2