Hi,
Thought I'd share my findings with anyone else with 3 kids...I've a 2, 5 & 8 year old and wanted to fit them in the mini (my daily car) if for some reason we couldn't (or more likely - I didn't want to take!) our family 7 seat car
Maxicosi Priory XP + 2 x "Bubble bum" booster seats - all our other boosters are too wide, these are inflatables and great as they mould to the contours - the head rests also line up perfectly
It's definitely snug

- I suggest only doing it if your kids get on o.k.!