You dad is responsible for his own choices. He is trying to put that responsibility on you and your mom, which is really unfair, but also pretty typical for an alcoholic who is still not dedicated to his recovery. He knows just how to suck you guys in by offering you the illusion of control because you've both been on this roller coaster with him for so long.
Take your mom out to lunch/dinner then go to an Alanon meeting together. It will really help make dealing with your dad much more manageable for both of you.