"I now know that the mother in law is trying to indoctrinate him. I am not sure if I should mind too much..."
Yes. Mind. VERY MUCH.
You're working with a slight handicap, as your son is so very young, he cannot 'filter' out false information at this time. However, if there is ANYTHING you can do to prevent cult indoctrination, please DO IT.
You don't want to hear, "Dad, I'm not going to college; I'm going to pioneer instead!! Oh, and by the way - I can't talk to you anymore..."
Best results to you...
Zid