I had a similar situation with my dad before he passed last year. When with dad, I would never let him drive and was always nervous when i know he was. Because I saw new scrapes and small dents whenever I visited him. He had major foot surgery, which let him with half a foot on each leg, but still refused to give up driving. Declining health put him in a wheelchair, but he still refused to give up driving. We were at a point, where we were ready to pull the plug on this driving he did, but his health took a turn for the worst and he just couldn't any longer. I was relieved but yet saddened. Because I know my dad, who was so active all his life was near the end.
It's a difficult situation to be in and I wish you and your family the best in dealing with dad. God be with you, for He will show you the right way!
