The OP said he wanted to go as a family. How exactly do you get two older teens to feel part of the family if they are in their own truck the entire time.
CB Radios. (or FRS or Ham) We've used them (or rather, the kids have) on trips with friends' families. The kids love yakking back and forth.
As for older teens, how are they going to feel part of the family if they don't get a chance to participate (i.e., drive)? Yeah, they can take turns, but why not let them each drive one vehicle?
There are a couple of LR folks hereabouts -- a father and son -- who each have their own Land Rovers. They do trips together, each in their own vehicle.
The goal, in my opinion, should not be to get everyone out there, somewhere, simultaneously, rather it is to be together in one place at the same time, enjoying and experiencing new things together...
I'm just not convinced that cramming 4 big kids plus mom and dad into one vehicle is conducive to family enjoyment. (Actually, having grown up as one of 5 kids in both a full size van and smaller Citroens, I know it's not.)
Sure, there's something to be said for making the journey part of the experience, but there's also something to be said for making the less interesting part as quick and painless as possible.
Now, I wouldn't consider having my wife drive one vehicle and I another and splitting the kids between us while they're young, but once they're old enough to be able to, I can certainly see them wanting to drive.
One more advantage of dual vehicles is that you have room for the kids' friends (or sigothers). We have a 7-passenger minivan -- it only allows for two of my three kids to bring a friend.
Mind you, were it not that I already have a Land Rover 109" and a Disco, I wouldn't consider it, but I also wouldn't completely dismiss the idea of his-and-hers Defender 110s if I won the lottery, either.