Looks like you got a good example of double copy of the frizzle gene.
brittle feathers,
bald spots
and ingrown feathers that would course the red inflamed skin.
I had a friend that ordered frizzled Cochins throw a hatchery and had the same kind of thing hers whent all most completely bald with only a few sad little feathers here and there. Its skin looked like there wasnt even folicals for feathers to grow out of, Not so good in the Michigan winters!!
beware ordering hatching eggs or chicks from breeders too, it's alway good to take the time to make sure your new eggs or chicks are comeing from some one that is keeping the frizzled boys in a separate pen from their frizzled hens. I've seen lots of people selling eggs from mixed flocks with both frizzled Roos and frizzled hens mixed with their smooth feathered chickens. This would most likely give you a smaller chance at getting a frizzled chick and the frizzled chicks you would get would have a higher chance of being double gene frizzles.
That being said, I have noticed for what ever reason. if your flock get lice or mites they are the first birds to show damage. Telling you when to treat the whole flock and coop, and do a good scrub down. And tend to molt earlier and harder than a smooth feathered birds.
In my opinion if it's not molt and not bugs, it's poor breeding. I don't think I would waste the money for vet test that will most likely not help your flock
If you see a rash, flakes, bumps or crud growing, then you have other problems that a vet could help with. But I don't see that on your birds.