Blocking any unwanted posts

Facebook makes it easy to block. Go to their profile and select block (should be under the same area as add a friend (I'm being deliberately vague because Facebook moves buttons around all the time).

And for God's sake tell your family that someone is threatening you so that if he does get to them, they'll know he's horrible and they'll put his revelation in its proper place -- the trash.

Also, report his profile to FB. You're being threatening. They will take action.