The Charlie/Novel Trilogy
While not the official name of the trilogy, this book series takes place in a different continuity from the original FNaF games. While the books do share similar names and events, it's not made to "solve" anything in mind. Some elements and characters from these books do appear in the later games and Fazbear Frights. The books are indeed canon as they are written and approved by Scott, but the timeline does not align to the games or even Frights.
The first of the FNaF books ever to be released. It was originally exclusive to Amazon before the publishing deal with Scholastic, which helped to make the book more widely available.
The Scholastic re-release only changes the cover and fixes a few typos.
The second of the trilogy and the first original FNaF book published by Scholastic that is not a re-release.
Despite the fact that Nightmare is on the cover, the story features the "Twisted" animatronics, which are very different from the Nightmares.
The third and final book of the trilogy. Which takes places after Charlie went missing from the second story.
The Funtimes make an appearance in the book. Strangely, this black Funtime Freddy appears in Ultimate Custom Night.