totally mystifying car insurance question

Does anyone know anything about car insurance?
I own two cars and share the insurance with my DD.
She has a pretty good driving record and mine is
excellent. We live in town don't drive much
and the small cars are 1997 and 1995 - not new.
We used Geico and it was supposed to be cheaper
It costs over $1400 a year to insure the cars.

A friend (who has twin 16 year olds) added them to their
ins. She claims that the increase in premium for
each child was only $100. DD doubled my insurance.
No one here can believe the rate she got. She claims that
it is just for teachers. Has anyone ever heard of this?

Who do you insure with and why?
Geico is not so cheap .....