Two things:

First: some of those people you perceive as being devout have had those same doubts and made similar decisions, so don't feel like you're all alone. Look at the world around you: is it easy to be an open atheist where you live? It may be hard to see it now, but there will be signs. Look around in church when everyone else has their head down with their eyes tightly closed and see who else is looking around with their eyes wide open.

I went to Catholic schools in the 80s and 90s, and almost literally none of the people I stay in touch with from school believe a word of it anymore, or believed/took it seriously in the first place. Perhaps ironically, the most devout believers I know today went through public schools. I was lucky, I suppose, in that our Catholic schools were incredibly thorough with science teaching. In high school we had monks teaching Physics, Chemistry, and Biology, and I think the only times I heard those dudes bring up "God" was either reverently in school assemblies, or in vain when something exploded that wasn't supposed to be exploding.

Second: uhhh... I forgot, but it was probably some sage and profound wisdom that was going to change your life and rock your foundational perspectives. Some knowledge too enormous and revolutionary to take in all at once... Which is kind of what you need to realize about your family and friends when you debate or discuss these things with them.

You were in possession of the same information they still rely on but you made a different judgement about its value. It was something that naturally happened for you, and while it may seem obvious to you, me, and everyone else on this board, it doesn't mean your younger sibling is just going to take your word for it right away, or that it would be easy for your older sibling to just accept that a core part of what makes up their identity is based on false premises. It takes a long time to come to terms with that kind of shift in worldview, perhaps as long as it takes to define one's personal identity in the first place.

People like you and me are lucky that we come to terms with the doubts we have about the faiths we were raised in while we were young. Faith in god can be a blessing for some people, but I think they are the exception and not the rule. Most have some struggle with faith in their lifetimes, and it's not often a short and simple process. Faith can be a thing that people will wrestle for decades, a source of anguish and guilt, maybe even self-loathing. Others will force themselves to believe a thing, they will find ways to convince themselves of "the truth." Then there are those of us who see faith as an obstacle that prevents us from being who we feel that we are, and maybe we even feel guilty or depressed about feeling that way. Some of us see god as a puzzle that seems to have no logical solutions... but suddenly it's revealed to be no more than an illusion, a parlor trick, a game of cards where the dealer deals himself cards from the bottom of the deck when he thinks nobody else is looking.

Try not to lose sight of the fact that we're all human. Enjoy your newfound freedom, because you are free, now. Free to think for yourself, free to believe or disbelieve what you want to believe or disbelieve. Free to never stop learning, to never give up on your dreams. The Universe exists, we think, and we are almost completely lost within it, shown to be so small and temporary as to be completely insignificant, yet at the same time knowing this our lives take on new significance. I find value and meaning in knowing this, a comfort that religion never let me be comfortable enough to feel. "I exist, I am not alone, and I have never been alone."

TL;DR, you rock, be real with other people, do unto others as you would have them do unto you, have patience with your family, don't steal unless you're playing baseball or basketball, don't kill unless it's online multiplayer in which case pwn, dress for the job you want and not for the job you have unless you want to strip, do not taunt happy fun ball, always try to see from the other's perspective, and don't ever forget who you are.