The Oxford Guide to English Grammar is a systematic account of grammatical forms and the way they are used in modern standard English. It is designed for learners at intermediate and advanced levels and for teachers, and is equally suitable for quick reference to details or for the more leisured study of grammatical topics. The emphasis is on meaning in the choice of grammatical pattern, and on the use of patterns in texts and in conversations.
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.