Introducing a man, a woman said “His mother is the only daughter of my father”. How is the man related to the woman?

If 'T' is the father of 'P'. 'Q' is the daughter of 'P'. 'S' is the daughter of 'R' who is the mother of 'Q'. Then how is 'T' related to 'S'?

Pointing towards a photograph, Raghu said, 'She is the only daughter of my mother's father’s only daughter'. How is the lady related to Raghu's father?

Alka introduced a man: “He is the only son of the father of my sister’s brother.” How is this person related to Alka?

‘B’ is the brother of ‘C’, ‘A’ is the sister of ‘B’. ‘E’ is the brother of ‘D’, ‘D’ is the daughter of ‘A’. How is ‘B’ related to ‘E’?