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You don't have to take everything from the bible literally to be Christian, there are lots that do but I think even more that don't. You seem to have found something that makes you happy so I would say stick with it, learning about other religions is great but you don't have to pick up another to find satisfaction in your own. (Also as far as I am aware you can be a new age Christian but I'm not really sure that Wicca blends all that well)
I think that a good way to bring up your concerns with your mother is to ask her what she believes in, ask her about how things she does may come back to haunt her and how she feels about it, ask her if the retribution could harm you or your sister (it can, and this is a pretty low card to play against a mother but you may open her eyes, but only use it if you find that she is trying to enact revnge through her religions) Above all don't seem condemning, ask questions, be open and listen to what she has to say (I don't know your mother she may get irate but if you stay patient more likely than not it will blow over) Show a continual interest and that you care and I'm sure they'll understand.
I think you're coming from the right place on this. 3nodding I hope you find what you're looking for here.
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