Complex sentence: Kupperberg's brother, Paul Kupperberg, also works in the comic book field as a writer, editor and executive, though Paul has worked primarily at DC Comics, while Alan's comic book work has been primarily for rival Marvel Comics.
Split into simpler sentences: Kupperberg's brother, Paul Kupperberg, also works in the comic book field as a writer, editor and executive. Interestingly, Paul Kupperberg has worked primarily at DC Comics, while Alan's comic book work has been primarily for rival Marvel Comics.