Hypothetical: Say I am rich and I have an 18 year old son that is at fault for a car accident that results in multiple deaths.

I'm sorry to tell you that the answer to your question is complicated and some of the possibilities require information you haven't provided.  I can, however, provide some general information.  The owner of a car is not usually liable for the negligence of a driver.  There are some exceptions:  if you gave the car to someone you knew to impaired or a habitually dangerous driver (this is called negligent entrustment) or if the driver was on an errand for the owner or for the household when the accident occurred, the owner might be responsible.  Even if this is one of those exceptional situations where the owner is responsible for the driver's negligence, actually collecting a judgment against an individual over and above the amount of insurance is extraordinarily hard.  Bankruptcy will wash out such a judgment, and this is the route that most defendants in this position take.  At the end of the day, it is very, very rare for an auto case to result in a payment by a defendant him or herself (as opposed to his or her insurer).  I hope this helps.