That's a good sign.
I was reading a thread from Nambroth a while back, she said she found a vet who could test for MD through a blood sample. I am not sure if you have those facilities available close by.
Normally, the bird needs to have a necropsy done to be certain if it is or is not MD, but I found it interesting to read that someone was doing live testing.
Hope the little guy turns the corner and comes good for you.
As the other person asked, have you wormed them at all? A good worming treatment won't hurt the rest of the flock.
I can't offer much on the sneezing or runny noses, I have never had that issue. Lots to read about with respiratory illness on here though.
Good luck