If the kid causes a major accident and he is underinsured by his custodial parent is the other parent who makes none of those decisions also held responsible legally? please advise.
You don't automatically have liability as a parent of a teenage driver. If you are an owner of the vehicle, you have statutory liability for your teenager's negligence by virtue of the fact you own the car. The statutory liability is $15,000 per person, $30,000 per incident maximum for bodily injury and $5,000 for property damage.
If the teenager owns the vehicle themselves and there is no independent negligence on your part, you are not liable for the damage he/she may cause.
Personal Injury Lawyer
the non-custodial parent will have no personal liability as he/she is not the registered owner of the vehicle, unless it can be shown that he/she did something affirmatively to contribute to the cause of the accident.
General Practice Lawyer
To start, make sure that the collision has been reported to the insurance carrier so that they can start evaluating any potential claims against the child. It would be very difficult to link a non-custodial parent to this collision for purposes of pursuing damages. If sued, the insurance carrier will necessarily provide a defense attorney for the boy and work to cut off potential avenues of recovery.
In no way am I offering you legal advice, and in no way has my comment created an attorney-client relationship. You are not to rely upon my note above in any way, but insted need to sit down with counsel and share all relevant facts before receiving fully-informed legal advice. If you want to be completely sure of your rights, you must sit down with an experienced criminal defense attorney to be fully aware of your rights.