DS2 has been hit the second worst, and is currently on his third round of anti-bs, and has a cough that just won't budge.

It's a non-productive cough, and is no longer violent enough to make him chuck (it calmed down a bit after starting this round of anti-bs) and is no longer causing him to wake, but is still lingering. It's a barking cough, no wheezing, no constriction, throat no longer sore, ears clear, nose no longer snotty, etc.
Did you have him tested for Whooping Cough? Only asking because my dd had a cough which was exactly as you've described, it turned out to be WC.