Alcoholics like to have codependents and enablers around them. Makes the illusion possible. Parents are the worst kind of enablers to have. Their love (and sometimes guilt....you never know what kind of parents they were or whether they blame themselves for the child's issues) can blind them completely....which give the addict free reign to manipulate and use them.
You have no control over anyone in this situation but yourself. Let it go. Try to detach. Take care of you.