For any medical thing, I always want to stress: VET! Best thing you can do as step 1 for a sick snake is call the vet.

For the mites, I personally used olive oil over mineral oil as recommended by the vet at teh time. Was recommended as healthier with same effects and easier to clean up. That said, nothing wrong with mineral oil to the best of my knowledge (and I don't know everything). The betadine bath is good, but can be over done in a way, so I reserve that for minimal use, if at all, varying on the situations. It's been years and I haven't had mites, scale rot, or any other reason to do these things, so my only thought is use betadine sparingly and try a different oil. Also, have you used the Provent-A-Mite product before instead of all-natural products?

For the scales: If I am reading this right, I had something like this happen a long time ago for some boas. Different reasoning and situation, but the thing to note is keep them and their enclosure CLEAN. Use real bedding, not newspaper, and spot clean well. If a big poo or pee happens, the newspaper may not absorb it all and their sensitive scales are then laying in it... But also bedding can keep stuff around if poor spot cleaning, so do that well. I used newpaper when mine had the problem and the vet scolded me, but that said the newspaper worked and I didn't have the problems I was warned about. Keep the humidity where it needs to be, not too low and not a puddle for a cage; This is important because some places (i.e. where I am) are dry in winter and the humidity is hard to get exact. The skin and scales can get too dry and be uncomfortable for the snake, and too wet can lead to other problems. Since they are stressed from this, also good temps all around just like if treating other illnesses. Minimal handling until they are better. Minimal other stresses as you don't want them rubbing too much nor stressing in general. Do not over do bathing (call a vet for recommendation on the amount) and don't over do the betadine baths either.

I have more, but not knowing your exacts compared to what I had happen, I cannot easily put the rest. Instead I will say again: Vet. Mine was a situation where a vet was 100% needed. Yours may not be, but you don't know until the vet sees what's up.

Good luck!!