those characters specifically, about Edward being a vampire and Bella being a...moron, etc.
It was starring the same characters, just all sexed up. That is what fan fiction is! (well, not the sexed up part.) Even the author admits this. Stephenie Meyers admits this.
It started as Twilight fan fiction. This is a well-known fact. Saying "Bull Crap" doesn't make a fact any less of a fact.
The Fifty Shades trilogy was developed from a Twilight fan fiction originally titled Master of the Universe and published episodically on fan-fiction websites under the pen name "Snowqueen's Icedragon". The piece featured characters named after Stephenie Meyer's characters in Twilight, Edward Cullen and Bella Swan. After comments concerning the sexual nature of the material, James removed the story from the fan-fiction websites and published it on her own website, FiftyShades.com