As others have said, doubt you will get 3 bikes in any car with seats up, let alone all the other stuff…Mondeo is clearly bigger in absolute space and useful space than A6.
Went to measure up some cars last weekend – might be useful to you
Audi A4 (11 plate so current model; the previous one is much, much smaller)
– boot floor with seats up – 97 wide by 103 deep by 70 high; full height 55cm forward from sill
– seats down 170 long by max 120ish wide between doors; height at least 70 for most of length, seats don’t go completely flat
Audi A6 (this was an 11 plate so the very last of the previous shape)
– Boot floor area with seats up – 104 wide by 114 deep; height approx 70; full height starts 40 forward from boot sill.
– seats down 180 sill to end of seat backs; max width approx 130; seats don’t fold completely flat, height approx 70 for full length of boot
Mondeo (brand new car)
– seats down boot floor basically a rectangle 175 long by 110 wide by 80 high
– didn’t measure width between doors on Mondeo, nor length of boot with seats up
– seats go completely flat, no real slope at rear window)
Passat (previous shape – 07 plate – but the newer ones are really just a minor facelift)
– seats up 100 wide (didn’t measure length) x 78 high
– seats down 125 between doors x 175 long – at least 75 high for length of car; no real slope at rear window.
Octavia was visibly smaller than Passat so didn’t bother measuring. Superb will be similar to Passat as IIRC it’s the same platform/ bodyshell.
I need to look at E-class and maybe V70s soon.