I think the car liability issue is a red herring. It is like worrying that you could be liable for an accident if your car is stolen. Teens allow unauthorized drivers in their parent�s cars all the time. Accidents happen all the time. So, where are all these lawsuit-bankrupted parents?

I would worry more about the real risks present here and not seek to invent new imaginary ones.

married for 40 years
DS - 38, autistic, lives at home
DD - 37, married and on her own
DS - 32, still living with us