Why do you have to drive in December? Someone is bound to be ill then. The weather will suck. I’d do it in the early fall or even summer.
That's roughly when they forsee being ready to get their kids' stuff. I'd seriously doubt, given their economic situation, any earlier, but it certainly could be delayed until the Spring. I just thought a southerly route would help. Maybe I-20 would be better than 40 once we're beyond Texas...
I also might add that in planning road trips, I come up with several contingency plans - hence my post: looking for good suggestions!