Groups, by default, do not show the email addresses to any roles other than Owner. To make addresses visible to Managers as well:
1. In My Groups, find your group and click on Manage to view the Group settings.
2. On the left side, expand Permissions and click on Access Permissions.
3. Find View Email Addresses.
4. Expand that drop-down list and click on Managers of the group.
5. Click Save.