One of our greatest family trips ever was a trek to Montana and then Wyoming. Started out flying into Helena and rented a van and drove up to Glacier National Park for several days (Going to the Sun Road). Then we headed back south to Jackson Hole/Grand Teton National Park for a few days and on to Yellowstone to end. People at Glacier apologized because it was 82 and "so hot" in late July. Regardless of your agenda, you should have a great time.