The "Members" group is one of the default groups in Nabble. You would not have created it yourself and it can't be deleted through the normal Nabble interface.
The Manage Users screen only needs to be seen by Administrators. They don't affect the interface seen by the ordinary user. Very few forums even implement the "Members" group and fewer still need more than one or two more types of user. It would help if you could explain why you need so many groups that you have a need to re-order them.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.