Im guessing you are a fullgrown woman that live in your own apartment and have your own life? Your decisions are yours to make. Your brother is trying to control you. He probably belives he´s doing this out of love to you and God.
Tell him that shunning you wont change your ways or they way your are thinking. You have your own relationship with God, that has nothing to do with with your brother.
Tell him you love him, but you have to live your life, not being controlled by his whims.
I know this most be so hard, and the easy way out of this is doing what he wants. But in the long run you haven´t solwed anything. Soon he will find more things that annoy him, and you´ll lose part of who you are everytime you give something up. I don´t really understand why he wants you to delete you fb account, he should be more worried about your connection to the ex-jw groups.
I wonder why he don´t ask you what you belive in and try to teach you the "truth" or atleast open up for a disscution about your belifes. Its like curing a headache with pill that only hides the sympthoms.
I hope everything will work out for you. Take care