One thought specific thought: on the way out (or possibly the way back), consider stopping at St. Louis, particularly the St. Louis City Museum. Your children will almost certainly love it.
And some more general thoughts:
Your guess is as good as mine as to what the wildfire situation in Glacier (or elsewhere) will be like next summer. This summer, of course, was exceptionally rough. I think as a general rule it's good to have some flexibility in your plans, at least as regards places where you don't need to make reservations far in advance. (Yellowstone, for instance, would fall into the latter category.) Also, don't forget to factor in time for mundane everyday things that one doesn't need to worry so much about on shorter trips: things like doing laundry and grocery shopping and that sort of thing.
It sounds like you're getting ready to have a fantastic family trip. I hope it all works out well for you. No matter what you decide to do and where you go, there will be many things you will skip or not be able to see, and that's OK; you'll also see and do and enjoy a lot.