We have driven from NJ for the past 4 years with kids of varied ages (on different trips we've had kids of 9 months, 14 months, 19 months, 26 months, 3 yrs, 3.5 yrs, 4.5 yrs, and 5.5 yrs. I always bring a lot of things for them to do and the kids have done great. We try to stop at rest areas for lunch where they can run around a bit. The DVD player is a life saver after dark when they can no longer see to color or play.
Personally, driving through the night doesn't work for us. We did it once and never again. DH drove while I was supposed to rest, but I was afraid he would fall asleep at the wheel so I couldn't sleep. So, we both ended up exhausted, whereas, DD was ready to go because she slept just enough to have some energy. A good night sleep helps everyone, so now we take the trip in 2 days and it is much easier.
My kids have recently discovered the aquadoodle character mini-mats and they are great for the car. You fill the pen with water and they color the pictures with the water. When they dry, the mats are ready to be colored again. No mess! At 14 months, my little one did like to suck on the pen, but it is only water in it so it can't be too bad for them.
With two grandmas in the car, I'm sure your little one will be entertained just fine!