Raman pointing to a lady, said, “She is the wife of my son’s only brother.”…

Concept: In blood-relation puzzles, unless stated otherwise, a person's “brother” or “sister” is a full sibling — they share both parents. So if a person X has an “only brother” Y, Y is also a child of X's father and mother.

Application:

1. Raman's son has exactly one brother — call him B. Since brothers share the same parents, B is also a son of Raman.

2. The lady is described as “the wife of my son's only brother,” i.e., the wife of B.

3. Since B is Raman's son, the lady married to B is married to Raman's son.

4. A woman married to one's son is that person's daughter-in-law, so the lady is Raman's daughter-in-law.

Cross-check: Tracing the family tree — Raman is the father of both his sons, one of whom is B; B's wife is the lady in question. This places the lady one generation below Raman, connected to him only through her husband, not by birth. That rules out being Raman's own child or Raman's own spouse, and rules out a sibling-level tie to Raman as well.