I'm sorry about your step-daughter, Star. That has to be as hurtful as it is disappointing.
I got pretty lucky, in terms of having a Christian upbringing. My parents took us to church when we were all really little (I have four siblings), but they quickly got tired of the hypocritical thinking and politics. So my mom taught us from the Bible at home. We read a chapter every Sunday and then talked about it. She never discouraged us from any ideas that we might have brought up, since she's always believed that if God made us, he made us think, and therefore our thoughts are just as relevant and right as anyone else's. She was always big on religious tolerance, and my dad was too. So when I came out to them as a Pagan, they were hugely supportive. They said that it might not be their path, but if I was happy and felt spiritual fulfilled, then who were they to judge? Christ never did (They actually said that to me the night I admitted to them that I was Pagan. One of the many reasons why I love my parents, lol).
My husband is agnostic, but his family is fanatically Christian, so we know that if we have children, we aren't going to be able to avoid having our kids exposed to it at some point, especially if they spend any time with his parents. My hope, though, is that between my husband, my parents, and myself, they may learn not to swallow everything they hear. The ideal situation, yeah. I reckon that's a bridge we'll have to cross when we get to it.