You must include the names of any contributors whose name appears on the cover image in your metadata. They should be listed exactly as they appear on the cover. For example, Stephen L. King is not the same as Steve King. If you would like to list additional contributors whose name do not appear on the cover, you can feel free to do so. For the most professional look, check out books of a similar genre on other sites and see which contributors are listed, as it can vary.