We are looking for group membership changes since they were created (or as far back as possible), who made the change, who was added/removed from the group, and when. Is there an option in Enterprise Reporter for this.?
Sorry I afraid that while Enterprise Reporter can track basic change history for groups, if turned on, which tracks changes such as add or removal of accounts and the associated date and time, that is the limit of the change history for groups.
Please take a look at Quest Change Auditor which should met your needs as this product is specifically designed to track changes and has detailed information.