Eh, with cars you can only be driving one at a time so it doesn't make sense for insurance to double or triple just because you now have two or three cars.
With family members, they are all absolutely living in parallel and at the same time.
I've owned 5 cars at one point, and dropping or adding cars never changed the amount of the premium attributed to the other cars. (That is to say adding car 5 was an increase similar to adding car 4, for example.) I never understood why, seeing as how I can only drive one at a time, but I've always just assumed this is customary.
