I was just about to say the same thing about the shavings.I never get tired of duckling pics!
They are young, so the sneezing could just be the shavings. They will get used to it.
If you don't want to test fully removing the shavings, you could cover them with a towel/cloth/old t-shirts (no strings or frayed edges) for a couple days and see if it helps. I usually keep mine on puppy pee pads for the first week or two, before adding the shavings. And I try to keep the shavings in the "bedroom" half of the brooder, and out of the "kitchen".Soggy shavings are such a pain. Your ghetto set up is fine! Anything to lessen the mess wins my vote.
They are dusty.
