JC - for a while when I was young and stupid I ran a small outfit doing 4x4 tour guiding up there. I ditched this about 12 years ago in favour of bike touring but still have many contacts in the 4x4 industry.
The most important thing for your family to decide is whether they want to do the self drive thing in a hired 4x4 or would they prefer the higher end (in product as well as price) pampered and fully provided for setup.
If they want the self drive thing, they should join into the overland forum (google is your friend) or the T4A forum where they will get fantastic support.