Your parents viewpoints are set in stone. They grew up in a different world, and most do not forward into today, they live in the past. The Cleaver family mindset.
To be quite honest, they'll never get it. All you can do is not get in the middle of the chaos.
If it were me, I'd just give your Dad a heads up and leave it at that. It is their choice, their money.
You can only work on your issues, your direction...they have lived their own life on their own terms, there really is nothing you can do.
My parents are in their 80's so I am familar with your delimna, but I have learned to butt out and go forward with my life.