Oh lol op, do you have siblings?
Our intervention attempt with my grandpa went like this:
"he has ruined his new car from every angle in a month. He didn't even know what he had hit in two cases. He lives on a street that kids play on and he travels to his summer cottage 500km away alone with no concept of a phone. He needs to stop driving or I'm not bringing my kids to this street." I said to my father, his brother and both of their wives..
After listening to two hours of screaming from my mother about me trying to turn them into the chauffer of the old man, and the sons turning from understanding the issue to down right mean about my take, I gave up and called my grandpa's doctor the next day.
He lost his license in the next checkup and I got shouted at till the day he died. Just be prepared. It will be nasty.