I used to do a little fire restoration work. All ductwork was torn out, AHU was replaced. Any ducts that could not be replaced for whatever reason was spray painted to seal any smell. Any ducts that were left were very small sections such as a small wall stack or something like that. Also any remaining wood that was smoked up or slightly burned that wasn't replaced should be sealed with a paint. I believe everything was sealed with an oil based paint. I can't remember exactly as it was about 12 yrs ago and I have MS as well and can't remember what I did yesterday. Think my first call would be the insurance company then a lawyer if things aren't fixed. Good luck