Two cars is definately BETTER.
1) In case one breakdown, the other one will come in handy.
2) You father and mother can go to their separate golf and shopping
schedule without argument over who should drive today and who
should take taxi.
3) When you passed your licence, you can get to drive TWO different
cars to impress your girlfriends. Trust me...this is a very very
important factor.
Maybe just ask your father to upgrade his car to the one that he
really likes, maybe a Lexus GS350.
No point getting a super luxury merc S-class or BMW 7series, a car
is after all a car.
IMHO, your parents are well-to-do, and status symbol are usually
not very important for old people who already has teenager
childrens.