First of all tell me what has changed in these two years and suddenly there is so much difference between all of you. You can blame the planets but also you need to understand and respect his viewpoints. You know the youngest kids are always considered the brat of the family always, you know why, because everyone things that he/ she is still a child. Many children who are young in the family hate being dominated and not taken seriously by everyone, everyone suggest that he is a child.
I feel this is really what you need to address, because now he is not a child any-more rather treat him equivalent or at least as an adult. Therefore I suggest you become his friend rather than his elder sister.
Another things how we look at God is entire personal. There is nothing in this world which is the best method to Know God. You have your ways which may differ from my ways. Some people like going to temple but some dont. I feel your brother does have feeling and respect towards God, but he does not show the way you may do and it is natural and there is no way you should disrespect it.