How is my grandfather’s only child’s only son related to me?

How is my father’s sister’s only son’s sister related to me?

A man showed a boy next to him and said – “He is the son of my wife’s sister-in-law, but I am the only child of my parents.” How is my son related to him ?NephewCousinUncleBrother

Introducing a boy, a girl said, “ He is the only son of my mother’s mother”. How is the girl related to that boy?

My mother’s sister’s husband’s only son’s sister is related to me as –

How is my father’s sister’s only son’s sister related to me?NieceCousinSisterAuntNone of these