Change to white mail...
Kick his asz
Kick his *** and reverse the tables.
Face the blackmailer and tell him to go ahead and do whatever he feels he needs to do. Even if you try to appease the boy, he will always have something to hold over you two.
Well, how is he blackmailing you? What? Does he have pics of you making our or something? Call the police. What he is doing is called EXTORTION. Do you really want your girlfriend to be victimized?
So...let him tell them. She should tell them first. If you love each other, why hide it? Why go sneaking about?
So, do not let them. They can try all they want but if you two love each other and are dedicated to each other, shout it from the rooftops and do not let anyone stand in your way and take your happiness from you. Family included. Man, if my parents chose a husband for me, I would have ended up shooting him in the face. Sometimes family does not always know what is good for you. YOU DO.
Tell the police.