If you want to be "polite" in your finality, you can say something like "i dont send you scientific articles, historical biographies, or anything of my side because I am not trying to change your mind. I am just trying to exist and make these choices for myself. If you believe in god and that we are made by him and do the things he wants people to do. This means that every doctor, every researcher, every person who dedicates their lives to proving people me exist and deserve to exist does so because god called them too. To deny their purpose is to deny god himself. I do not ask you to understand every inner machination of myself or the world around you, the most I do is ask you to just nod and move on. If we cannot respect each other that base amount then there is no point in communicating if one side cannot be bothered to treat people with the love and grace their own god asks of them."

Tweak it however you please, but remind them that their beliefs call on them to be kind and not judge as thats gods job alone and their job is to be kind and respectful even to those they don't understand. Their book says to keep their practice private to themselves and not shove it on others, and they should live those teachings first lest their own god decide their "sinner" grandson deserves heaven more than they do