We (DH, DS7 and me) will be going to see them for two weeks in December. It's a 12 hrs flight, 7hr difference (it is relevant).
We would stay one/two days in their home city and then the plan was to all go to the coast to spend Christmas there, where one of DH's friends will be too. It should be a 2hr flight.
They now suggested DH could drive instead. It's a 10hr drive. Not a big deal allegedly, as we could do it overnight 
DH feels bad because they are usually happy to go along with our suggestions, so thinks we should just accept, but AIBU to think this is way too inconvenient? Plus, I do not understand what is the reason behind it (they haven't said)