Collection of relationship riddles

A man is looking at a picture of a man on the wall and states, "Brother and sisters, have I none, but this man's father is my father's son." Who is the man in the picture in relation to the man looking at the picture. This riddle appeared in the Simpsons. Here's the relevant clip. Here's the solution and its explanation.

If Teresa's daughter is my daughter's mother, what am I to Teresa? Here's the solution and its explanation.

I am your mother's brother's only brother-in-law. Who am I? Here's the solution and its explanation.

"Someone called me on the phone," explains Jack, "and when I asked with whom I was speaking, the person calling was surprised I didn't recognize the voice, since the mother-in-law of his mother is my mother. I didn't believe what the caller was saying, since I have no siblings." What is the relationship between Jack and the caller? This puzzle, and a derivation of its solution, is given on page xvi of Train Your Brain: A Year's Worth of Puzzles, by George Gr├Ątzer.