Need your help please!

So, tonight my 12 year old brother told my super religious parents (dad and step mom) that he believed in the Big Bang theory and was not sure if he believed in God. Now, they live in bible belt Texas and are heavily involved in the church. I, myself, am agnostic-atheist. But I am cool with whatever anyone wants to believe. Thing is, my step mother involved the church and now they are filling this poor kids head with guilt and lies about the "devil having a hold of his soul".

I tried to explain to her about the big band theory and how many scientist believe different aspects of what that theory means and how it started. All she can hang on to is the few scientist who debunk the theory. Now, my point is not to argue whether or not it is real. I want some advice on how I can handle this situation. My brother believes in his heart that God is not real, how can I help him support his beliefs without indoctrinating him with atheism (My aim to remain objective and help him evaluate both sides of the issue)?

And furthermore, how can I convey some sort of (in my head reality) objectiveness towards her? How can I show her that he is in fact right without her thinking I am calling her "parenting/ beliefs" into question, even though I kinda am? This whole thing is fickle, and I will answer any questions needed for insight further into this situation.

I would really love to tell her she is a lunatic and that he, at 12, is smarter and far more objective than she is. This, however, would not help him and would serve me no purpose in my mission.

Tl;dr My brother told my parents he might not believe in God, shit has hit the fan, how can I help her to understand and help him know he is not wrong for feeling this way?