An auto insurance policy normally terminates upon the death of the policyholder, usually by the request of the estate so. A refund for the remainder portion of the policy that has already been paid for is returned to the estate.

There would probably not be any coverage for the son or other relatives to move the car if they are not listed on the policy.

Your brother-in-law's son should contact the insurance company to find out for certain if he would have any coverage to move the vehicle or if the policy ended with the passing of the policyholder and he needs to request the refund and find other insurance for the vehicle.