I say there is no need to go out of your way to let your beliefs be known, but if questioned, feel free to tell them. Family or not, they need to respect your right to have your own beliefs, so if they get pushy, stand your ground and tell them to back off. If they don't respect your right to believe what you want, then they don't respect you as a human being, and I see no need to keep people that don't respect you in your life.
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
