Tow Vehcile for expands 17.56 OB

Other than something that will fit you all in most important is towing and load capacity, you need the 3.5t tow cap, 350kg tow ball and as much carrying cap as you can. So a vehicle GVM of at least 3t with a GCM of 6t , many will say not needed but a family of 5 means a load and you will need every Kg you can get so you don't have to always comprimise.
I would go low mileage 2nd hand or demo, they usually have the extras, most bugs ironed out and you save a heap of dollars especially if you don't have to add bits to them.
A 3.5t tow cap vehicle loaded up for a trip most times has tow cap left to drag 2.8t or so around behind it, you don't want to sitting on your max weights all the time...
Have a look thru http://expandasdownunder.com/forums/tow-vehicles.31/ for heaps of views on the various tugs around, Nissan drivers are biased though.

Welcome to the forum,

I have an Everest - it is hands down the best vehicle in that range. If you goggle car advice you will be able to read the reviews
The Everest has also won numerous awards over the past two years.

They are an awesome tow car and family car!

Have you done a spreadsheet with all the extras you want to put in the tow vehicle, it's surprising how quickly it adds up, bull bar, tow bar, tow ball weight, 2nd battery, fridge, fuel, anderson plug, spotlights , water, people, mtn bikes etc. I chose a dual cab tray back ute with payload of 1150kg once i'd added everything up.