Can my husband or myself be held responsible for the actions of my son who is 19?

Your son reached the age of majority in the state of North Carolina when he turned 18.  Should he have an accident causing damage in excess of the liability limits of your policy, he would be responsible for the difference.  If he has no money, they could garnish his wages if he is working.  Your best bet, in general, or if you want to protect your son, is to carry sufficient limits of at least $100,000/300,000 and possibly add an umbrella policy which will kick in when the auto policy's limits have been exhausted.

Your state probably has a vicarious liability provision.  And that would hold you, as the owner of the car, liable for the negligence of the driver.  In states where vicarious liability is a part of the law, both the driver and the owner of the car are responsible for the accidents that are caused by a driver's negligence.  This is done to afford the person who was injured an ability to collect adequate compensation.

In addition to vicarious liability, you could also be held negligent if, as the owners of the car, you had a duty to (for example) change the tires or repair the brakes, but didn't. And that failure to repair was the cause of the accident.