Hiya Ashley
Family can be very funny about all of this. My sister is full-on supportive to my face, yet my mother tells me that she's recently seen tantrums from my sister relating to my transition. And both my sister and her husband have this batty idea that telling my really small nephews about me would leave them traumatised.
Putting aside the religion and sinning bit, which I think is simply crazy, I think it's incredibly difficult to understand what's going on in a hostile family member's head, or to be able to develop a positive strategy to counteract it. Disappointment, social embarrasment, revulsion are all things that people deal with in different ways. It's much easier to reject than to look at onesself and reevaluate one's prejudices, and it's my opinion that many people are phychologically and intellectually incapable of analysing and putting aside their prejudices.
I know you are hurt, but rather than burn bridges we should just try to drop the barriers on our side in the hope that the storm will blow over. I totally get your need to unfriend your sister on FB, but rather than treat it as an act of aggression and exasperation, I hope you will see it as a temporary need for protection.
Sigh, the things that are sent to test us, but be positive that there are still family members who care for you!
Hugs
Julia