Answer: Demodex sp. and Sarcoptes scabei
This was a fun case because of the presence of 2 different mites in a single specimen. As noted by Arthur Morris, "it's likely that Sarcoptes is causing the rash, though in some cases Demodex can cause Sarcoptes-like rashes."
Mites belong to the class Arachnida, and therefore have 8 legs in the nymph and adult forms, but only 6 legs in the larval form, when they are newly emerged from the egg. Although it's a bit hard to make out in the photograph, I believe we have a larval Sarcoptes scabei mite in the bottom left of the image below, which helps explain its small size.
Thanks again to FloridaFan for donating this great case.