mites? also, porphyrin..?

Question
My fiance and I have many ratties both with hair and hairless.
In one large cage we have Mr. Pimbz (hairless) who has always been prone to skin issues/sensitivity. In the same cage we have another hairless(well with course wiry hair that grows and sheds) and Pimbz' 3 sons with hair. Our main question is the 3 with hair have been itching for quite sometime at first we thought maybe they were "nipping" each other but have realized otherwise. They have scabs(you can only see them near their mouths and only know by feeling for them, they're not visible otherwise)almost "clustered." WE have looked for mites but have not seen any
,but they do have hair so I'm not sure if we're missing something. The other 2 rats don't really itch and don't have any scabs aside from the usually claw scratch. Are they more ways to check for mites? ALso, we have switched their bedding to see if it was that, it wasn't,we have the bedding that is great for Pimbs as well as the others (no wood dye perfume ect.). Any ideas on this?

And Pimbs seems to always have porphyrin coming from his eye (left one), by always I mean usually upon waking up. WE have treated for eye infections with terramycin applications. Pimbs is kind of a "lemon rat" meaning allergy prone and way sensitive to certain things. He is fine and happy other than the annoyance of having his eye cleaned out whenever he awakes. He isn't sick, he plays eats his behavior is as usual and he sleeps like he always has.

Any ideas on either of these would be greatly appreciated.
thank you

Answer
Well, good news and bad news.

Good news: Pimbs is completely normal. By completely normal, I mean that most hairless rats are prone to extremely sensitive skin and respiratory systems, which includes the excessive discharge from the eyes particularly upon waking.

Bad news: Yes, they all probably have mites. Clustered scabs near their faces, if they're red; is a huge indication of regular skin mites/lice. If they're black, its quite possibly mange, which is also a mite, just a different type. Either way, it can be treated with ivermectrin which can be bought through your vet. Your vet will do a skin scraping to confirm that its mites before they prescribe ivermec.