I do not have
experience with leg mites..... but my first step would be do massage some
diatomaceous earth into their feathers and on their legs.
Are the birds in a coop or pen? Do they roam outside? Do they have access to a dust bath?
If there is a coop or house that they live in I would strip all bedding, put in a dusting of lime and diatomaceous earth on all surfaces and put in all new bedding.
respirator masks
should be used when handling the lime and diatomaceous earth, and the birds should not go back in until the dust has settled and new bedding in place - as it can affect their breathing as well.
I would be interested in hearing other peoples methods for dealing with this issue.