These novels, titled Grey and Darker are the same stories as the first two Fifty Shades books, just told from Christian Grey’s perspective instead of Ana’s.
The Fifty Shades novels that became a phenomenon were written from Anastasia Steele’s perspective and words on a page are only telling the reader what the author wants them to know.
E.L. James has already released two other books in a planned trilogy that are sort of the other half of the Fifty Shades books.
The reason this can work as a book series and not as a film is because of the differences in the mediums.