To clarify, imagine that a child's parents are a same sex male couple. Is there anything in the above sentence that can differentiate between: "This is my father" "These are my fathers"
I'm full of questions but I should ask :) Why we should use hai(n) instead of hai.
This is an honorific हैं. When you want to show respect to someone, generally an elder, you use हैं ending that you generally reserve for plural sentences.