I don't see where religion is hurting your father at this point in life. In fact in his condition I would be afraid to try to convince him otherwise. It is just fine if he wants to believe in Jesus Vishnu. I don't think you have a problem, other than your Dad's condition. Maybe you should sit down and watch The Exocist together. That should be fun.
"On Earth as it is in Heaven, the Cosmic Roots of the Bible" available on the Amazon.