If I'm reading your plan correct, your husband will go with you until Denver. That will be a big help with driving. I really think 5 weeks is enough time for your plans if you just do your family/friend visiting a day or two. Many families go 'out West' with only 2-3 weeks of vacation time. You're young - so long drives won't affect you or the kids like it would for older folks. :) A few days in Yellowstone is much better than none. Not everyone has the luxury of spending a week in that park. The same goes for the other major attractions. You just do what you have time to do. You'll still be imprinting memories.
Unless you're in a good position to pay $14,000 for a rental I'd suggest buying a pop-up camper for the trip. Just about any car can pull it. There are some very nice ones nowadays. They are easily resellable after your trip. Good luck!