Okay so answer to your question - sleep deprivation can cause hypomania (which can lead to mania, which can lead to crashing into depression) so that is something to keep an eye on.

As for the family - my extended family is super religious (well one side of them). My dad's relilgious, his mother and siblings. Two of his cousins are hard core Southern Baptist preachers (they are brothers and one of them has a side helping of not so subtle racism going on there). And lots of other Southern Baptist relatives.

Is your Mom supportive of you being atheist (or at least not trying to convert you?) because if she is, I would talk to her. Write down a script and read from it if you have to.

Say something like - Mom I know how proud you are of me and how proud my grandparents are that I'm getting sober. Maybe you don't know this, but discussion of religion, especially with family members, makes me extremely anxious. Could you please talk to Grandparents and tell them I know they love me and want what's best for me and right now not discussing religion is best for me. Being anxious is a threat to my sobriety."

Or something like that. If your grandparents don't seem to understand you can go with - "mental illness and anxiety are extremely personal, what makes 1 person anxious doesn't make another person. And right now this (religion) is a trigger for anxiety so I'm trying to avoid anything that makes me anxious". - This being relayed by your mother (or whoever you trust).

And if someone brings something up, say "I'd rather not discuss this right now." Change the subject and if they persist then find something pressing to do.

You didn't say what kind of retreat it is -but I'd spend summers with my aforementioned super conservative family at the beach. Different houses but we'd always end up over at their house, with Rush Limbaugh on the radio and not so subtle racist remarks and sexist crap. It would get too much so I'd say, I'm going to take a walk. Although that can be tricky becuase sometimes people want to go on a walk too. So I'd say, "I think I'm going to go read" and slip off and go for a walk alone.

As a total last resort, I would throw out the guilt, "If you really love and support me you discuss religion with me/let me be by myself/accept that this is how I am."

But that's a guild trip and I'd only use that as a total last resort.