My dad has definite signs of dementia but Drs day he’s fine?

He has had a brain scan that shows shrinkage, he has made numerous bad decisions, one of them being driving onto the beach and getting stuck there because he thought he could park there. He has had memory tests and phsycology tests but Drs say he’s fine but just basically a bit cantankerous. He forgets important conversations, he tries to contact old friends that he hasn’t seen for decades and some of them he stopped seeing because he fell out with them but he doesn’t remember. He’s not the man he used to be but he’s a danger to himself because he’s so mobile and has no diagnosis so no one can stop him. He’s angry and expects everyone to serve him and his needs but at the same time won’t let his children do anything to help him because he thinks we’re trying to get him locked up in a home and take his driving license away from him. We don’t know what to do for the best and the only thing we seem to be able to do is watch him decline and wait for him to do something stupid.