See the "Formality and Respect" section in the Family Tips and Notes:
In formal situations and for respected people (including all elders), plural versions are used in every context. For example, with पिता (father): मेरे पिता भारत में हैं - My father is in India; उसके पिता अमेरिका से नहीं हैं - His father is not from America.
I have trouble knowing whether the English should be "drinks" or "is drinking" (same with other verbs). Is there a general rule that can be briefly summarised by some kind person here? Don't worry if not possible. I can look it up in the tips (or elsewhere) when not using my mobile. Thanks in advance if possible!