I am under the same boat. My dad is one of the most intelligent people I have ever met yet he still clings to beliefs that I feel deep down he knows are silly. The two times I have ever talked about religion with him he immediately gets defensive even though I have never tried to de-convert him, I've just tried to show how contrary his beliefs are with his scientific mindset. He never pushes his religion on anyone, including his kids, and he doesn't base his life or politics on it. So then what is the harm? The real problem with religion is that many people believe it's their duty to push their beliefs on everyone else. So I agree with what has been said here already, if he's not pushing his beliefs and his beliefs aren't harming him, let him believe whatever he wants.
Even if the open windows of science at first make us shiver after the cozy indoor warmth of traditional humanizing myths, in the end the fresh air brings vigor, and the great spaces have a splendor of their own - Bertrand Russell
