K.B.
When my boys were young we made a long trip to Colorado. I was concerned about them getting car sick (since I did as a child) and my doctor suggested giving them Benedril to prevent car sickness. The upside was they slept for a couple of hours! I also made grab bags. I had gone to the dollar store and bought a bunch of new toys and put them in paper sacks. I also put a lollipop or some other long lasting candy or snack in some of the bags. Whenever they got restless, I would let them choose a grab bag. They loved this, since they rarely got candy otherwise.
The seven month old is more of a challenge. When my boys were babies, I would string cheerios or fruit loops on a string to make a necklace. That way they did not spill them all over the car. Also, as babies, they were really fascinated by common objects. On a long trip, I would just gather a bunch of kitchen gadgets, cheap tape measurer, old cell phone and other items from around the house. They have toy bars made for infants now. I bought one for my niece and she loved it. Check out the resale shops for this type of item, especially if they have the ability to attach various toys other than the ones that come with it.
On long trips, we always try to plan on numerous rest stops and even an hour at a park or in bad weather, MacDonald's play land. Seven or eight hours a day in the car is about the best you can hope for and hope they will nap a little. Good luck!