Child restraints in a 7 or 8 seater vechile?

ok here is a question for everyone. I had a capsule (strider dlx) installed by RTA (NSW) yesterday and he installed the capsule behind passenger (i have a 8 seater Carnival/Sedona) how ever the passenger seat was that far forward it be lucky if a 12 year old could fit in it. I always though middle was best especially if back seat has side airbags. They installed my 2 year old AHR maxi rider in middle. I how ever ended up changing it my self as I explained the man how is my disable mother suppose to access the front seat and isn't middle safer and was told no, so I ended up putting capsule in middle (but might need one of those buckles that tighten seat belt) and sons car seat(he has buckle to tighten seat belt) is behind driver so if I ever have to pick someone up the passenger side is vacant, I unbuckle my son and get him to crawl past capsule and he comes through to passenger side and i can easily acess capsule from passenger side too. So what would u do if u had a 7 seat or 8 seater vechile?