Who is liable for Minor Driver?

My 17 yr. Old son has obtained his learner's permit and has driven his father's car, which has expired registration tags. I can only assume that the car is uninsured, as well. Dad has sole legal and physical custody.

I have warned my son about driving any car that has expired registration. This past weekend, he mentioned that he'd had a driving lesson in his dad's car so I reminded him again of the consequences if he's pulled over; or worse, involved in an accident. His response: "Dad's already looked into it. He'll get the ticket - not me." I told him I'd looked into it too and that I was told that the driver will definitely be cited and it's up to the police officer as to whether or not they'll cite the owner as well.

I don't know whether my ex has considered how this could affect our son's future. DS would more than likely lose his ability to get a license and will also be stuck with an SR-22 filing on his DMV record (certificate of insurance required for 3 years), not to mention, outrageous insurance rates.

In addition to being concerned about my son's safety and liability, if there was an accident where injuries were sustained by another party, could that party sue me (I'm the NCP) if they can't get anything from the CP (Dad)? Dad has no assets or wages to attach. I believe that if there was no vehicle insurance and my son sustained injuries, he'd be covered through my medical insurance (but I need to verify that too...)