It is notable that Islam orders us to be kind and loyal to our parents. Referring to this, Allah Almighty says: “Thy Lord has decreed, that you worship none save Him, and (that you show) kindness to parents. If one of them or both of them attain old age with thee, say not ‘Fie’ unto them nor repulse them, but speak unto them a gracious word.” (Al-Isra’: 23)
Thus, we are to show all types of good treatment, respect, and honor to our parents. However, if one’s parent is sinful what conduct one should keep with him/her? This is what the prominent Muslim scholar, Sheikh Muhammad Iqbal Nadvi, Imam of Calgary Mosque, Alberta, Canada, and Former Professor at King Saud University, Riyad, Saudi Arabia, has to say on this: “Every adult in such situation should deal with their parent as a father/mother and behave towards them in an Islamic way by visiting them and inviting them over at your home.
However, what an adult must do is they must not help in providing them alcohol or bringing it to the home. Also, if such adult already has kids, they should discuss this situation with the kids; talk to them about this sinful act and explain to them how they should behave as children towards their grand parents.
I would like to advise to take the example of Prophet Muhammad, peace and blessings be upon him, with his uncle, who was a Mushrik (polytheist), which was obviously worse than drinking alcohol as a deed. Yet, the Prophet, peace and blessings be upon him, kept good relations with his uncle and showed him the due respect.
Also, one needs to discuss the issue with the alcoholic parent in an attempt to bring them back to the right track. Try different approaches and never stop calling upon them to give up drinking. May Allah help us!”