Dan, there is a perfectly valid answer to that riddle...
And your brother being your dad...a little comedy of mine:
I was slowly getting older and confused. So confused that I gave up
when my son was born. I'll tell you about it. Won't take long: the
next four short paragraphs. But get ready: quite a few "steps" involved.
I meet a widow, who lives with her step-daughter. I marry her. At the
wedding, my father meets the step-daughter, falls in love, and marries
her. So now my wife is my father's mother-in-law, and my wife's step-
daughter is my step-mother. Plus I am the step-father of my step-mother.
YOU AIN'T SEEN NOTHING YET.
My step-mother and father lose no time and a boy is born. Now this guy
is my step-brother. And as this guy is the son of my wife's step-daughter,
this makes my wife this guy's grandmother. Also makes me the grandfather
of my step-brother.
IT ONLY GETS WORSE.
You guessed it. Now my wife gives birth to a baby boy. My step-mother is
now my son's step-sister and also my son's grandmother since he is the son
of her step-son. And my father is now the brother-in-law of his grandson..
or is it the step-brother-in-law?
NOW FOR THE CLINCHER.
All this clearly shows that my wife is my father's mother-in-law plus that
I am the grandfather of my step-brother. Get the picture? Therefore, I am
my father's something-or-other-father-in-something-or-other which makes me
my own grandfather. Which is why I'm taking me to McDonald's. I guess I'll
be able to give myself grandfatherly advice over a Big Mac, Medium Fries
and a Large Diet Coke.
1- I mailed a firm of experts in family reconstructions a request for a
family-tree, along with a cheque representing their fee; the cheque was
returned to me.
2- Afraid that some other boy might be born and in all probability make
me my own great-grandfather, I asked my father's mother-in-law for a
divorce; she agreed quickly as she was aging as quickly as I was.
3- My father, who was getting younger and younger due to these births,
quickly found a new husband for my former wife: my older brother.
4- Update: yes, a boy was born out of this new union and who knows: I'm
now probably my own great-grand-uncle!