As I understand it, red mite is a parasite of birds and does not infect humans or other mammals - it is host specific. Mites will run onto a human and are a little itchy, but they cannot feed and survive. I assume it is the same for sheep. Sheep scab mite is a different sort, not carried by hens.
When hens have a red mite infestation, the mites themselves will be found in the house, not usually travelling around on the bird in the daytime. This means that it is the housing which needs to be cleaned - creosote or a flame gun do a good job of getting rid of the mites.
Ivermectin is not licenced for use on poultry except under the control of a vet, and the dose is just a very few drops depending on the size of the bird, so for you to treat someone else's hens with the chemical could all go horribly wrong.
We treat our birds with Diatomaceous Earth (is that what you mean by 'Damascus' earth?) It can work well with a few applications, as long as the source in the houses and perches is sorted first.
I take it the bantams live loose in the stables? Don't use a flame gun then unless you can take the perches outside