Brothers and sisters have you none but that mans brother is your brothers son who are you?
You quoted the Riddle incorectly. The real riddle quotes,
"Brothers and Sisters I have none, but this man's father is my
father's son." You contradicted yourself saying you had no brother
and then saying that your brother has a son. The way the real
riddle works is as follows:
Disregard the Brothers and Sisters part, that has no
significance to the riddle whatsoever and is only there to throw
you off. The second part works like two statements. The first being
"This man's father" which clearly showing that the man has a
father. And "is my father's son" saying that the father has a son.
Think on it....Your father's son. THAT"S YOU! haha. I hope this
clarified the riddle to you. I had the same problem when I was in
High School. Enjoy teasing your friends with it and if you have any
other Riddles, please don't hesitate to send a few my way.
Semper Fi