I would encourage getting a legal opinion from an attorney about auto insurance and liability as it relates to your particular policy. May vary by state. Normally, insurance will cover s licensed driver. So be careful canceling coverage on someone who still has access to the car keys. If the driver is cognitively impaired, family members might be held civilly liable for damages if they harm someone.

While it seems desirable to get someone to understand why they shouldn’t drive and to accept it, that really isn’t required. The priority is preventing them from driving. Even if someone seems to accept and agree, that is often a momentary thing. They will often forget and the entire discussion will be required the next day or the next hour. So getting them to get it, doesn’t really bring any benefit. It might be a verbal discussion every day. It can continue for years. But, the important thong is that they don’t drive. If it’s not feasible to keep the keys away, I’d get a legal opinion from an Elder law attorney about getting court authorization to legally prevent him from driving.