You can download a file with a list of your group members and their email addresses to a CSV file.

To export a list of group members, you must be a member of the group and have the Who can manage members permission. To see member email addresses, you must have the Who can view member email addresses permission.

Export

1. Sign in to Google Groups.
2. Click the name of a group.
3. On the left, click Members.
4. Above the list, click Export list.

The export of group members will not include a display name.  It will include a nickname if the group member updated their display name in their own My membership settings.