Gday Mate, I looked at the video and there are a few probs, which it sounds like you are now onto. The kitty litter substrate is no good, it is very dusty and will create more problems where powderlike dust and sticky mucous is concerned,
Put him on white butchers paper while you sort the mites out. The RI is the most important problem then the mites, so treat that first before any chemical mite spray. You can wipe him over daily with a cooking oil (almond, olive) to treat mites naturally while he recovers from the RI, Clean his newspaper daily, and wipe his tank out with water or oil at night. That keep them at bayuntil he gets his energy back. The tines of his tongue are there, just stuck with mucous and will come good. Burrowing and thermo regulating (moving on and off the basking site) is normal behaviour and a good sign. keep his temps up, keep him at 30 degrees 24/7.
Also very important... after you handle him, jump straight into the shower clothes and all. thoroughly soak your clothes to kill off any mite on you. Do not handle or work on him or his tank without doing this.