Your plans are a bit ambitious for your timeframe I think to be able to really enjoy yourselves. I40 is 10 hrs. straight south on I75 to Knoxville. I always plan our trips for 65mph and divide miles by 65 for a time reference. I suggest you go online and order travel guides from the states you will travel through. They are great references for points of interest and most have maps that are more helpful than an atlas. Its also hard to suggest things not knowing some of your family's interests. Get the guides and have everyone go thru them and pick out something they would like to see or do. Don't push things so hard that all you do is drive.