I -- and maybe others here -- am still not clear on the sense in which you mean "a group" of books.
If you mean a group of books that follow on each other, either telling one long story that was just too big for a single book, or at least related stories centering on the same characters or otherwise related, that's called a "series". Like, "the Harry Potter series". I've always found it curious that if there are exactly three books in such a series, it is called a "trilogy", but there is no commonly used word for a series of two books or four or any other number. (Nobody says "bilogy" or "quadrilogy".)
If you mean a group of books in the same general category of fictional writing, like mysteries versus romances versus science fiction, etc, those are called "genres".
If you mean a group of books that are physically collected in one place, like all the books that I own and that I keep in one room in my house, this is called a "library".
"Chronicles" and "saga" don't mean a group of books. The American Heritage Dictionary, for example, defines "chronicle" as "1. An extended account in prose or verse of historical events, sometimes including legendary material, presented in chronological order and without authorial interpretation or comment. 2. A detailed narrative record or report." I've never seen a definition that implies it must be in multiple volumes. It's true that many fantasy series these days call the series as a whole "The Chronicles of Irving Milqbiscuit the Barbarian" or whatever, so maybe the word "chronicles" is coming to mean a series of fantasy novels, but I don't think it's a recognized meaning now. I don't think I've seen that usage outside of the rather narrow field of fantasy novels. I've never heard anyone refer to "The Chronicles of Perry Mason" or "The Chronicles of Diesel engine repair manuals".