With fourteen exceptional pieces, this is a cornucopia of music by the great composers from the famous films: Branagh's Much Ado About Nothing, Henry V, Romeo and Juliet and Hamlet together with William Walton's outstanding score for Laurence Olivier's original Henry V. The book also includes works by the nineteenth-century giants Tchaikovsky and Mendelssohn.
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.