I remember you going through this exercise the other year............
maybe should have brought that Jheep..............
in answer to your question (in easy to understand engrish) - your Hilux will not be legal to tow the 17"
unless the car is empty and so is the Van
(only because the weight of the front Bar, roof rack, winch, ball weight etc all comes OFF your allowable 2.5T (2.8T dont remember) towing capacity)
hard to understand Legal explanation = Car GVM + Van GVM = GCM
Car GVM (Gross Vehicle Mass) (Total weight of your car & passengers & load)
+ Van GVM (Total weight of your fully loaded Van)
= GCM (Gross Combined Mass) (Total of Both)
this, in your case with the Hilux will be over your allowable GCM
even if it was just under your limit, you would then be pulling the guts out of the engine to start moving, keep moving and trying to stop.........
not a good idea IMHO
the thing to watch out for is that most of the new generation of dual cab utes have similar GCM even though they have varied Towing Capacity
if funds permit, best be looking at the Pajero / Jheep / Landcuiser / Discovery - Range Rover to get the Maximum GCM and be safe