One of the previous posters, made a good point. If either of your is too tired, stop and have a proper sleep, if only for a few hours.
DW cannot sleep in any moving vehicle (car, RV, Plane, Train etc). We have lots of family stories about her hallucinations when she is over tired.
The way we make it work it she takes the early shift and drives for up to 8 hours with a stop every 2 hours to stretch our legs and walk the dog. I can sleep anywhere and sleep through the first few stops. After 8 hours I drive for up to another 8 hours, then we stop for at least 6 hours sleep. We still make good time, but are better rested when we arrive.
We have done a 24 hour push, but it was not pretty and we will not do it again.