We have a Captiva 7 and can fit three seats across. A Qld Ambulance Service employee fitted all three (albeit it took a bit of arranging and rearranging), so I know it's ok, even with that middle seat being a PITA

We bought the most slimline booster seats we could find - Infa Secure - and we have a rear facing Safe and Sound Meridian. The boosters are next to each other, with the SandS (obviously) on the other side. They are all touching each other, but I find if I pull the booster nearest the window toward me a little, it gives me enough room to clip the seatbelts in.

I love my Captiva

ETA: The QAS employee (who's been fitting car seats for ages) said the foreign-made SUVs were the hardest to fit the three seats, but Aussie made cars were easier. Not sure if this helps one iota ...
They may have changed their seats? We brought our 7 seater LX brand new in 2007 and we couldn't fit any of our seats in the middle because it was too narrow. We measured it and it was only 30cm wide. We only need two car seats anyway so it wasn't a problem for us, but it meant that DD2 had to climb over 2 car seats to get into the middle of the seat which was a pain at times.