Hmmm... wish I could be there to see/listen to them. Three weeks old, they need about 80-85 degrees. I think that given the ages and sneezing, I would separate the sneezers from the others, though it's probably too late, you never know.
Make sure they keep eating and drinking, keep them warm. Other than observation, not much I can tell you. Oh wait, one thing- newspaper isn't very good for chicks- wood shavings (NOT cedar) or paper towels would be better. Gives their feet a better grip and prevents spraddle leg.
Good luck, I hope they are fine.