How about this:Not likely to work.
"Ok people, gather around. I am now an atheist, I don't believe in your gods or goblins anymore until you show me evidence. I am still the same person, compassionate and caring, but I am tired of everyone superstitious nonsense. If you want to do any good for society you will join me in seeking evidence before superstition and encourage scientific discovery and progress. End of topic, have a nice day."
Walk away like a boss.
You are right, not likely to work.
Here is why I think it will work. You show confidence yet open to door by offering to work together to find solutions. It's like dealing with children:they will see you are successful and upbeat without the need for superstition in your life. This happened to me, others came to me secretly and said help me, I wish I could lose that superstition too!!! I recommend to them to read Richard Dawkin's book called the God Delusion.
Now most are so brainwashed they may fight back. If they try to re-open it, shut it closed. None of their business what you believe. If they persist hit them with the absurdity of their beliefs (40 days of rain to flood the earth, God needs the devil and uses him as a scapegoat so he can put you in hell, evolution is a fact, etc...).
Then for a second time walk away like a boss.
Rinse and repeat.
So what if the family kick the person out on the street and take away their college fund, shun them and attempt t destroy their lives? This thread regards people in that situation. Please bear this in mind when making suggestions about how to deal with real family situations. One can escalate more easily than retract. Once an interlocutor is considered 'enemy' they are in a difficult situation. The end game may be 'fuck you I'm an atheist' but that isn't a good place to start a negotiation.
I agree with you, clearly one has to know their situation to determine how true they can be to themselves. I suggest using common sense in this matter. It is a very sensitive topic for some people who need to use God as a coping mechanism. If you live in a situation where your existence is in danger for not believing the same ideas as your providers, then lay low. If you can afford to tell them you don't believe, then you can do it! Or do like most people and say nothing at all! It's no one's business. If people force you to go to church and they ask you do you believe in an invisible cosmic puppet master...just really "sure..what ever". Determine your level of confrontation.
At the time I could afford to point out the inconsistencies in religion to my providers, so my situation is lucky. I started by saying..."if the end result is eternity in hell, don't you think it would be fair for the creator to provide more compelling evidence before hand?" The door opened from there to argue with my cousins about the nonsense of their ancient beliefs. We still bicker today at the dinner table....lol. You will NEVER change their minds. Don't waste your time.
But take care of your well-being first. I hope one day in the future, by 2020, facts will triumph over superstition. But humans run by emotion more than logic.
I suggest anyone get atheist support: read Richard Dawkins, watch youtube videos, this forum is amazing place to start.
In the end do what ever makes you happy.