"My father's sister's husband" — hearing this relation, Tanu says this person is her "mama"…

Why

Tanu has spotted that this is an uncle by marriage, but Hindi, unlike English where one word 'uncle' covers every case, uses a separate word for each side of the family, and choosing the wrong side gives the wrong word. 'Mama' is wrong here for two reasons at once: mama means your MOTHER's brother, and he is a blood relation, not an uncle by marriage at all. Trace the chain one step at a time: my father's sister is my 'bua' (a paternal-side relation), and her husband is my 'foofa'. That is a completely different word from mama, which belongs only on the mother's side. Test it: walk the relation slowly — father, then his sister, then her husband — every step stays on the father's side, so the answer must be one of the paternal-side words ('bua', 'foofa'), never a maternal-side one ('mama', 'mami'). Her brother is right: this person is your foofa, and getting the exact word right means tracking which SIDE of the family each step stays on, not just that it is some kind of uncle.