I would suggest something like the 100 series landcruiser, seven seater, and if setup right can be super economical towing even the biggest vans. The Man did one to tow a big van around Australia, and I am sure he said its fuel usage was 11 litres per hundred kilometres. Seriously. On the highway.

What else, oh yes. I would recommend them joining up with an online forum or two (if they are tech savvy), such as overlander dot com dot au, or Australian 4wd. The overlander one is all about big trips and vehicles, and could be very useful for them, not just in terms of choosing a vehicle, but finding out some special places to go to (and more importantly, how to get there!)
Cheers, yes Dad is very tech savvy - and he adores researching so I will put him onto those two sites.

I think the Kia Sorrento was on his list to look at - Landcruiser too - the family have always had good luck with Toyota's so is good they are so prevalent over here.