How can one deal with an 80-year-old father who is addicted to drinking alcohol, and with whom all attempts at persuasion and admonition to abandon this habit have been unsuccessful?

Pray for your father's guidance and repentance, and be patient with him, for Allah is the one who guides hearts, and do not despair of his reform. Continue to advise him gently and kindly, and it is preferable for the advice to come from a virtuous person. Do not expel your father from the house, for that is an act of disobedience. Abandoning a father may be permissible for a legitimate Sharia benefit, otherwise there is no benefit in it.