There's a section in this site called "Friends and Family of Alcoholics" - you guys should check that out.
You can't cajole, plead, cry, beg, manipulate or threaten an alcoholic. It has to come from inside of them - a desire to change. I think you can love them while protecting your own health, and tell them your own truth - maybe even steer them in this direction (this website).
Believe me, I wish there were some sort of exorcism you could do to remove the things which possess us and compel us to act in the most insane, bewildering and hurtful ways we do, but there isn't.