Hello.
There is public transportation from points on the Peninsula, like Menlo Park to San Francisco. Easy peasy.
When is your trip?
I used to work in Menlo Park.
If you change your mind about car rental, check out Club Sportiva
. One of the owners is a friend and fellow car enthusiast (including Porsches) and he and his wife moved to SC about 2 years ago.
Anyway, the Porsche enthusiast community here is very welcoming and we'll help you however we can.
Please contact me via PM and I can try to provide some additional suggestions for you and your family.