I really don’t think it’s ich. Foxfaces develop a protein in their slime coat which makes them resistant to ich:
https://www.sciencedirect.com/science/article/abs/pii/S1050464810000197
You already treated for velvet and ich with the copper. It’s unlikely for them to get this rampant after that treatment.
I personally think he’s having a viral/bacterial infection. And you said you treated with prazipro a few times? That should take care of any eye flukes as well.
This is definitely one of the most weirdest cases I’ve seen. Definitely take my advice with a grain of salt because I’ve personally never experienced this type of issue on any of my fish, nor have I seen this type of case on the forums.