Who do you think are the "kings and queens" of these genres?

POP : Elvis Presley ( he was the first popstar, and he is the biggest selling solo artist of all time)
and the Queen would be mandonna, even though I don't like her.
ROCK : King is impossible to choose. Queen probably Tina Turner.

RAP/HIP-HOP : Jay z Queen of rap either Missy Elliot or Nicki Minaj.

SOUL : James Brown or Ray Charles. Queen is Aretha Franklin.

R&B : Impossible to say either King or Queen because R&B has changed so much since the 30s to today.

ROCK 'N' ROLL : Elvis Presley and there is no Queen.

queen of pop: (in order)
madonna
janet jackson
whitney houston
mariah carey
celine dion
britney spears
beyonce
lady gaga
rihanna
katy perry

You have it almost right. The only one I'll disagree on is Marvin Gaye, the honorific belongs to James Brown, who held before Marvin Gaye. Wanda Jackson on her induction into the Rock Hall of Fame was called the Queen of Rock and Roll, as well the Mother of Rock and Roll. Honorifics such as those aren't to be transferred from one artist to another. I'll add two more names to the list.

The King of Country Music is Roy Acuff, his Hall of Fame plaque reads as such.
The Queen of Country Music Kitty Wells, her plaque in the Country Music Hall of Fame reads as such.