Welcome,
Alcoholism is a family disease, your mother is as sick if not sicker than your father. You will never convince your mother to take a stand to not enable, she is weak and codependent and of that mindset to stand by her man....no matter how it effects the rest of the family.
You have a choice, either go down with the ship, or, jump in the life boat and head for the shore.
There are bounderies that you can set with your mother, she appears to be the pivot point that you are trying to work around.
Read around the family & friends of alcoholics, lots of great information about bounderies, that if properly enforced can become the oar you need to paddle to the shore.