My family still thinks I'm a Christian and I'm not sure at this point how to proceed.

To understand my current situation, I must explain the somewhat paradoxical position of my parents. On one hand they're intelligent (dad got a masters from Princeton ), well traveled (mom spent three years In Portugal ), care about the environment and raised us in a radical, controversial method known as unschooling which involves learning by exploring your own interests at your own rate. On the other hand, they're fundamentalist Christians who go to church every Sunday, listen to Rush Limbaugh and would have thought it heinous if we so much as dated in high school.As an unschooled student, the only friends I had throughout my entire childhood were my siblings and these two sisters who were our friends and who went to the same church.I never questioned Christianity at all until we (my siblings, friends and I) participated in our parents weekly philosophy group and began listening to a history of philosophy. Anyway, these lectures got me interested in thinking about things logically and rationally. Soon I realized I had no reasons to believe what I did. So, rather than started from a blank slate, I tried finding reasons to believe that to which I was already convicted. For example, the question of why there is evil in the world. Because God gave us the freedom to choose evil. And our freedom is more valuable than an enslaved perfection. But more and more, I began to find holes.I could not, and still cannot find a good reason to believe the Bible is God-sanctioned, or how prayer could possibly help something. (If something's good, we shouldn't have to pray for it to happen, and if it's bad, why pray for it?)Then I left for college and took a religion course and came to realize how based on culture religion is. Traveling in Europe (what used to be the Roman Empire ) has only strengthened this idea. Religions are also more similar than I had given credit.There's not a single moment I can point to and say that's when I stopped believing, but the idea has just seemed less and less probable. I've prayed to God and gotten no response. And the Jesus story, while beautiful, also seems like mythology. I guess I've stopped trying to work out if I believe the messiah story, because I'm trying to figure out bigger issues, such as what to base morality on. Is it subjective? Objective? Who decides what is good? What does "good" even mean?My family still thinks I'm a Christian and I'm not sure at this point how to proceed. I'm not an atheist, rather, as Socrates put it, "I know only that I know nothing." My siblings are my best friends and even my parents I can get along with really well. I don't want to lose that, but at the same time, I want to be able to live my life without slinking around or lying to them. (For example, if I dated someone who's not a Christian, or had premarital sex, etc.) When I talk to my sister she says stuff like, "on the weekends, everyone here (meaning college) just wants to go and party, and obviously I don't want to do that." As though, obviously, I must think partying is an abomination, too. Or when my sister asks if I've found a church to go to.I'm not sure how to tell them. I will be moving in a few weeks and will live in the same city as my sister, who's also my best friend. How can I tell her, or my parents, or my other siblings? Is this something I should do in person? Should I tell them outright, or just let it go naturally and not lie to them in conversation and let the chips fall where they may? Over the past few years I've been dropping hints that I'm essentially an agnostic, but it doesn't seem to sink in. I'm not sure who to turn to as all my friends are Christians. Any advice?