When I quit the seminary and left the church I tried to slip as quietly out the back door as I could. At this point my theology professors from college, many of my college and seminary friends, and most of my extended family know I'm an atheist. I officially resigned my membership with the SDA church almost two years ago. Now I'm an atheist blogger and I've talked about the SDA church on the Chariots of Iron podcast a few times.
I'm as out of an atheist as I can be, both with those inside the SDA church and everybody else.
If they set it up through the conference's estate planing office then they are required to include the church in the will with an equal share to each child. That's the trade off for the free service.
My parent's couldn't cut any of us out of the will for leaving the church since they would have to cut all of us. While it's good for that reason and made it easier for me as the youngest, I'm sure they feel like spiritual failures.
If it hadn't been for that added pressure I likely would have called it quits my junior year of college rather than after a year in the seminary.
You should ask your sister if that's why she's still in the church, if it is then try to help her to not live for your parents. She's an adult.
I agree with Andree. I keep it mostly to myself to preserve relationships. The two friends I have opened up to about it (and this is not including my husband) did not handle it well. At all.
Also, I'm an only child. I think this would devastate my mum.