Tonight’s update: the vet just checked out the flock. She found NO MITES!!! I have been applying DE directly to vents/under wings. Vet agreed no infestation at this point, and could not find mites in coop. It’s nighttime now. When the mites were at their worst, there were mites swarming vents.
Vet recommended continue DE treatment (she agreed it was effective!!) AND ivermectin drench (3-4 rounds of this) to eliminate mites through potential generations.
Just wanted to give update and let folx know our experience in dealing with these little critters. Thank you ALL for your help.