Sorry to hear your family is having such a rough go these last few nights. We are too - and for the same reason! My 4 year old has allergy induced asthma, but, despite only having outdoor related allergies, we seem to be experiencing the same cough every couple of months. That said, here are a few things we do in addition to those you already mentioned.
Push liquids - a lot of them. I take little guy to the grocery store to pick out his own juice boxes (which I typically don't buy, so it's a treat for him). He loves the looking at big bird, cookie monster, etc., and I'm just happy he's drinking a lot of something!
Elevate the crib/bed mattress. We usually fold a few bath towels and put them under the head of his mattress. It really does help with the post-nasal drip that irritates his throat.
People will surely doubt the following, but for us it does help. We limit the amount of dairy products during a cold. I usually limit or hold off completely his intake of milk, yogurt, etc. since it does seem to increase the mucus for our son.
I really hope these suggestions help - and sweet dreams to all of you :)