Princess123,  I am sorry you have such a person in your life.  It seems he knows how to contact your family.  I would go to each of them preemptively and tell them what is going on.

Block him, don’t take his calls, and stop all contact with him.

If he is threatening blackmail and you have copies of his texts to that effect then perhaps someone can counter-threaten him to say he is breaking the law doing that.

Otherwise, back away and let the chips fall where they may for otherwise he will continue to have power over you.

Mark