In a very real way you stand between your wife and your daughter. She is very vulnerable to indoctrination from any source, let alone her own mother. That doesn't mean you should attempt to indoctrinate her first; that's just as bad. It simply means that you need to be the voice of skepticism in any conversations about Ba'hai, or any other belief. It sounds like nobody else will be.
Of course you can't be there every moment. However if your wife privately tells your daughter things about the faith that would not convince you, firstly she's picking the easier target and secondly she knows on some level that her reasons are not sound, and is using them to preach anyway. Both are dishonest, and she needs to realise that. Her first act as an evangelist should be to convert you, not your daughter.
Pay attention to your daughter, that's the main thing. If you think she's not thinking about something the right way, it's your job to put her straight. That's just one of the things you do generally as a father; this is no different.
Though you have every reason to be concerned, don't worry too much. What probably started me on the road to doubt was the simple fact that my father, someone I respected and looked up to, did not buy into religious belief like everyone else (it seemed). He only bothered to tell me he was an atheist about once. Your mere presence as an unbeliever may well influence your daughter greatly.
Firstly, congratulations on your newfound independence and on increasing your self-knowledge. It can sometimes take a reprieve from the constant background noise of belief to even imagine an alternative to it, even if it's already your position deep down.
You seem to have a good grasp of your situation. I don't know what religion your family adheres to (from the Revelation reference I presume it's some kind of Christianity) or how devout they all are, but the sudden revelation of an atheist in their midst (especially for the first time) will doubtless provoke strong reactions.
It will indeed occur to them that you think they've wasted a lot of effort over the years. It works both ways, too; they'll think you're wasting the effort you've put in all your life. All that work to save your soul, and you're just throwing it away. The important thing is to emphasise that it is nothing personal. Your problem is with the beliefs themselves, not your family. Rejecting the beliefs does not invalidate everything you and your family have done with their church - the socialising, the charity work, the philosophical discussions. Conversely, though, the work they have done does not by itself make the objects of their faith (God, a resurrected Jesus) real.
Your parents in particular may feel they have somehow failed you, and God, by bringing you up to be the kind of person who could reject God. It's not their fault, because all they did was bring you up to think about what you are told and examine things on their merits. This prevents you from living in blind faith, and if you continue to believe you are the best kind of believer: one equipped to defend the faith. There was always the possibility that you would come to the opposite conclusion, and that's the risk. They might find this idea reassuring.
There's one thing I really need to warn you about. Your family may be intelligent, but I get the impression that they aren't terribly familiar with non-belief. They will feel a tremendous urge to try their hand at apologetics to bring you back around.
You expect this, but here's the thing: most of them will not be very good at it. You'll get the most facile, intrinsically flawed arguments in existence thrown at you as if they're irrefutable. They do seem that way to them, because they've accepted them without really trying to test them. Your very delicate task will be to respond to each one as simply and patiently as you can without getting frustrated.
I invite anyone reading this to share their own experiences of coming out to their friends and families as an atheist. It can be every bit as bad as coming out as a homosexual, so some mutual support is always welcome.