My 87 year old dad is sure he can drive, how can we deal with this?

I know 87 is pretty old to be driving, but is his only problem that he is getting over lung surgery or has he got mental issues?
Why did your brother take the car away in the first place? If you'all had good reason to stop dad from driving, then stick to your guns and sell the car or whatever. It's better to hear him whine and complain, even fight with you then to drive and kill someone isn't it? Gotta do what you gotta do sorry.