Wait I'm confused..... why are people saying Franklin can only store 2 cars at his hillside house?
In my game, I've stored 2 cars in the garage (the most that can fit) and outside on the driveway his first car (which starts off white) and his bike are always there.
No matter how much I do, I come back and they're always there.
Also, I've sometimes lost a random stolen car or bike during some activity, and when I go back to his house, it's there too, parked next to the driveway.
So there's 4 that can easily be stored there, and sometimes a 5th extra car that's not "mine".