If my father's wife has a car in her name only and she has a wreck and hurts or kills someone, can the other party sue my father?

This depends upon the state where your parents live.  Generally the person liable for damages that are the result of a car accident is the person driving the vehicle and the registered owner of the vehicle.  However, if your father and his wife live in a community property state, both spouses are responsible for debts incurred by either spouse.  So if your father's wife were to be sued for any reason, your father would also be named as a defendant in the lawsuit by virtue of the fact they are married.  If your father's wife were found to be responsible and ordered to pay damages, those damages would also be your father's legal responsibility.  There are only a handful of states that are community property states.  Since I do not know which state you are writing from, I cannot tell you specifically about your state, but this would be easy to find out by doing a quick search on the internet.