Hi Rachel, I doubt I have any answers for you, but I do know what is is like worrying about acceptance by religious family members.
My stepbrother and stepsister were both raised very religious Christians, and the only reason I think my stepsister might accept my transition is because I am technically not of her blood.
My stepbrother is a different story. He recently went on a religious trip (I forget what kind) to Indonesia and spent a month or two volunteering in a village with a very large transgender population. The experience opened his eyes to how the transgender community is no different than anyone else (except perhaps more certain in their life goals). Because of that trip I feel he would be much more accepting of transition.
Perhaps if you can find some church event that involves transgender people in day to day life and your parents see what my step brother saw, then maybe they will be more accepting...
I wish you the best of luck with your family!