Lan wants to be a detective just like Mindy Maple the heroine of her favorite mystery series. So when the mysterious Ms. Martin moves next door, Lan decides to investigate. On Our Way to English Guided Reader, Level R.
Various is the correct author for any book with multiple unknown authors, and is acceptable for books with multiple known authors, especially if not all are known or the list is very long (over 50).
If an editor is known, however, Various is not necessary. List the name of the editor as the primary author (with role "editor"). Contributing authors' names follow it.
Note: WorldCat is an excellent resource for finding author information and contents of anthologies.