What's my liability

What is the name of your state? Maryland

My 19 year old son was pulling out from a park and ride (my car, my policy).

An elderly couple barely brushed his front bumper, scraping off the front license plate. He was near the white line on the edge of the shoulder. They obviously went into a panic and turned into the curb on the park and ride about 90 ft. down the road, jumped the 15ft dirt divider and hit two parked vehicles. The elderly couple appear to be only bruised. But there is significant damage to 3 vehicles. However, the two vehicles parked in the park and ride were not parked there for commuting reasons. They were parked there solely to be seen for sale. There is a sign in the park and ride stating it is illegal to park there except to commute. The police did not charge my son.

Questions:

1.- Can I be sued beyond the policy amount if my son is a legal adult at 19.

2.- Any liability to the illegally parked vehicles. It was a Saturday and if they weren't there illegally the serious damage would not have happened.

3.- The elderly couple left no skid markds attempting to stop, they barely grazed my son's car and traveled a good ways down the road before jumping a good distance before hitting the other vehicles. Even the tow truck driver commented about it. The speed limit in the area is 40 mph.

thanks....