Prerequisite:
We have a Passat B8 and must accommodate 3 children on the rear seat.
Result:
It works, finally, because if you buckles with this booster seat, the child in the correct order, fit a Maxi-Cosi infant car seat, these booster seats (must in the middle !!) and a child seat class 3 in the back seat next to each other. For this seemingly intractable problem there is but one solution - yay, we have to buy a new car.