The New Interpreter's Bible is a commentary in 12 volumes plus the 13th being an index. It offers critically sound interpretation guided by scholars, pastors and laity representing diverse traditions.
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.
If you are in a moderate or liberal tradition and are looking for one affordable full-Bible commentary, this is the one I would get. If you are in a more evangelical tradition get the Expositor's Bible. If you want to be a well-balanced fair-minded teacher and preacher, get them both.