Should I give in to my father's emotional blackmail and guilttripping?

My father is a strict catholic fundamentalist. His siblings and him try to run the lives of every member of our family. Everyone usually yields, because when something is done not to their liking, they start sessions of guilttripping or blackmailing (you do not love me, if you loved me you would also love God; how can you brake your father's heart like that? you will never see your sister again, because you have bad influence on her) Lately, my cousin decided to "rise in revolt" against this holy terror. Among other things, she invited me and my wife (we are a same-sex couple) to her wedding. My father threw a tantrum. He said that if I attend the wedding with my "whore", he won't let my little sister attend the wedding... I am afraid that if we do come, the whole ceremony will turn into some kind of civil war.

It's not that I want to promote some "gay agenda" and "fight for equality"; in fact, I am not that pro-LGBT either.... the thing is that I want to start living my life how I want, I want to support my cousin in her attempts to live her life as she wants. We want to show my father (and his siblings) that they can no longer terrorize us. I'd really like to show him that his tantrums and blackmail won't work... but I am afraid of ruining the ceremony and hurting my little sister. What would you do if you were me?