I have trouble dealing with my uber-religious parents, advice please?

I am 31 years old. I live very far from my parents and generally visit them once a year, at Christmas. Everyone’s parents drive them nuts, but mine, especially my step-mom is REALLY religious. The whole area (Aiken, South Carolina) is super Chrisitian. I was raised Chrisitian, sent to Lutheran school up to 8th grade, but my folks got extra religious after I left home. I am now agnostic and have been since I was 20 or so. I made the mistake of telling them I wasn’t Chrisitian, which I’d undo if I could. It has really caused a rift between us. My dad is okay, we get along alright. My mom is the problem. She’s extra mega super religious. She’s also very emotional and overly sensitive. She is extrememly evangelisitic, and will proselytize as much as she can. Sometimes she tries to be subtle, which is annoying because she’s not subtle. She refuses to listen to me about anything even non-religious stuff. She opposes me whenever possible, despite usually being wrong. I have tried everything, talking to her about it,not talking to her about it. Trying to explain my side only makes her try harder to get me to go to her church. We used to be a fairly close family, I’d like to at least be able to spend one week a year with them and be happy. Am I foolish for even trying to have a decent relationship with these people? Any advice would be helpful. Oh yeah, on top of the rest I am unmarried and uninterested in getting married. I’m not gay but I’m pretty sure they think I am. My mom thinks marriage and babies are everything. She also thinks women are supposed to obey men and not think much for themselves, and I’m very much my own independant woman. Luckily she’s not after me for grandchildren as I have step siblings who have provided the grandchildren.