Jeff, I was in college and a "baby" sister in fourth grade loved simple math questions, like "Add two numbers and get twelve; subtract the little one from the big one and get two". I couldn't think them up fast enough for her.
In fifth grade she wanted nothing to do with them. I wondered if someone she liked told her girls don't like math.
Do you trust your sister to do the same, if she feels a need to?
If a bible thumper complains to your mother about you, will she tell you so and talk with you about the pressures she's feeling?
I hope so.
Patience is your best asset at your age, in my opinion. The urge to bust out of the demented lies of religion is overpowering sometimes. But if you are living in a conservative religious community, then your best bet is to bide your time. Just accept that you have to be a cultural Christian, go along with the motions of going to church and keeping up appearances. When you are older and wiser, and can see the whole consequences of coming out, then you can decide for yourself whether it's worth it to speak up. Busting up with your mother is traumatic and is best avoided if you can.
As for your sister, I would teach her by example to trust her own head about what is real, and trust her own heart about what we are living for. If she seems to be drifting into religious zealotry then distract her heart with emotionally fulfilling activities that aren't religious, and keep her head straight by presenting both sides of an argument to her. Good luck.
Welcome, Jeff! I hope you like it here! I'm finding it warm and supportive.
Since I'm the last person in the world qualified to give "happy family" advice, I'll leave it at the "welcome!" Please post often! I look forward to seeing you around the Forum.
Welcome Jeff glad you found us. As for being more open about your atheism take Michael R's advice and be patient.