Hm, not really. It is already implied with the verb passera and sounds very unnatural.

Vi passerar = drive on, not stop. But 'svänger förbi' = stop for a short visit.

Because the subject is 'we', so We are passing some other people's restaurant (their = deras). "Sina" would be used only when the Subject (They) are passing their own restaurants (plural). Or what sounds more natural: Hon passerar sin restaurang (or) Han passserar sin restaurang.

Nope.

Yes, exactly. :)

åker förbi means you're travelling by vehicle, but passerar means you're passing by any means.

åker förbi is probably more common, though both are fine. Please note that's just a guess, though.