This is a long thread, but I wanted to post, because I had a very similar situation happen when I was about the same age.
My mother is Lutheran, which is how my sister and I were raised. My father was raised Catholic but is now an atheist (as he has been for most of his life). When I was 11, they sent me to Catholic school because the public school sucked. Lutherans are pretty mellow (our church, anyway), and the state of my father’s soul was just never discussed. I just assume he believed as we did. At Catholic school I learned all about hell, and asked my mother if we were going to hell. My mother told me that the Catholics were a little melodramatic, that you don’t need sacraments, just belief, and that we were fine.
But it starts turning around in my head-- Daddy doesn’t pray. Daddy doesn’t go to church. So I asked him if he believed in Jesus, and he told me no. I recall being pretty devastated, and then making the mistake of telling a nun at school (who told me that my father would go to hell if he didn’t repent, which was awesome). I stewed on this for a long time. Eventually I asked our pastor at the Lutheran church about my father.
He told me that some people have a harder time believing, and that God has his own path for them. Some people need to see the face of God himself before they believe, but as long as they have lived a good and decent life, when they die and they meet him, he will welcome them with open arms.
My father and I are very similar, and while I never got to full athiesm, I did abandon Christianity in it’s entirety (which he said later he expected I would). He and I have had many conversations about how and why he came to his belief, and they were frankly more interesting than any religious conversation I had with my mother. The only difference between him and I is he sees no evidence God exists, therefore believes he doesn’t. I see the same lack of evidence, but am not entirely convinced you can prove a negative. There might be God-- I guess I’ll find out when I die. My father has said that he would be very surprised to find pearly gates, but he would not scorn indisputable proof.*
He told me that after my conversation with the pastor, who’s words have stuck with me all my life. It was an incredibly kind and useful thing to tell a confused 12 year old-- it was the only good answer to that question, because it absolved me of both my worry and the crazy idea I was responsible for my father’s soul.
The next year I transferred back to public school, which really was a good thing. As I became more aware of the history and the world I was having serious cognitive dissonance problems as I saw logical gaps in what they were teaching. This was something I really, honestly, needed to sort out for myself. Not having those issues all tangled up with my schooling was immensely helpful. I didn’t need my internal conflict about the nature of God dragged into the middle of my English class.
Best of luck. FWIW, my parents and their religious differences will celebrate their 40th anniversary this September. My sister and I both turned out fine.
*He’s also said of my mother, “One of us is right, and if it’s me, at least she’ll never know it.”