The Quasqui is a mini-SUV
Bigger and "safer" than your standard issue people carrier.
However...
VERY limited off-road capabilities

Good for mounting pavements with a bit of extra boot space.
Why do you want to spend extra on a SUV that isn't really good as a SUV?
To answer your questions:
a) NO
If it's safe family travel with extra boot space I'd go for a station wagon. Probably the Subaru if you foresee some dirt roads in your near future. Why spend a premium on a heavier car that isn't really more spacious or off road capable than a regular station wagon... not to mention, the handling and fuel economy will be way better with a station wagon.
If you absolutely MUST have a mini SUV, then I'd also recommend the Honda. It's the best mix of reliability/build quality/safety/fuel economy for the price you pay.
b) The eternal Diesel vs Petrol Debate.
it boils down to the following:
Does the premium you'll pay on a diesel model warrant the savings you'll see at the pumps?
The short answer: NO
You'll never make the difference in fuel savings... mathematical fact, not to mention the shorter service intervals on diesel cars.
However... it doesn't take into account the fact that you ache every time you swipe your petrol card. There's a level of satisfaction you get from doing over 800kms to 65litres of fuel... that only a diesel can provide.
You might not make the money back over the lifespan of your car, but you just can't beat that feeling of making it down to Durbs from Jo'burg with a quarter of a tank still to go.
So... to sum it up:
If you're a bean counter: Diesels are more expensive up front and will cost you more in maintenance in the long run.
If you are a fuel economy nut who likes some low down torque: Diesels are the way forward.