Thanks for the comments.

I went ahead and ordered the Marmot synthetic bags.
I saw a post by Earthling that finally persuaded me to go ahead and get the more moisture tolerant synthetic.
I just didn't want to end up in a 40'F, rainy, muddy situation with damp down bags.
That means the kids will each have to carry 18oz more than the Campmor down bags I was considering, I hate that but I also saved well over $100 in the difference.

Backpack = 3lb 11oz
bag = 3lb 8oz
---------------------
= 7lb 3oz

a little more weight than I wanted, but I still think we'll keep it all under
20lbs