Hi there mymatemax I thought I would register and let you know about my experience with this issue, So basically I have a little sister on life support with a wheelchair that we need permanently, this means she needs a team of four carers plus me and my mum, now the problem is we had a look at some 7 seater cars to see whether it would be sufficient for my sisters needs, turns out the wheelchair is far too big for a normal sized/family car but in the end we found through mobility a Renault Master (14 Plate) I know that It is a much bigger vehicle than the common "Family Car" but It's the ONLY vehicle that had the features to carry all my sisters equipment and her carers all at the same time and also the wheelchair, We got this Van from Motablility though I STRONGLY suggest you don't go for a Renault Master though as we have had the van down to Renault 7 times in the last two months for a Gearbox overheating problem that they've still not been able to fix..... So what I am saying is if you have no luck finding a suitable vehicle then going for a wheelchair accessible van may be your only option, (A non Renault Van) Maybe something like a Vauxhall Movano or something of Similar size, search the web for wheelchair accessible vans, I think Allied Mobility did the conversions for my sister and I think they work in Partnership with Motability (Could be wrong) We didn't pay any advance payment, Motability paid it for us as I'm not working due to health problems and my mum is disabled, I will post photos later, I just thought I'd post this as a suggestion because much like yourself with space and stuff we found it VERY difficult to find a Vehicle suitable for our needs, It takes a bit of messing around with Motability and Allied Mobility but in the ends it's really worth it, I just want to reiterate to you that I STRONGLY suggest you do not go for a Renault Master because we've had no end of problems with it but going for a similar Van size would probably help you out.
P.S. Our van has 8 seats and an isle/walkway for the wheelchair to be loaded onto the van inbetween the seats where Carers and Passengers sit, As I said I will post photos later and also private message you my personal number if you have any other questions or want to speak to my mum about how she got the van in place and got the funding....
Thanks Very Much and Hope to hear from you soon
David x