When you create a group you can limit the minimum votes to publish a story to the group. No matter what is the number (e.g 15), any story with any number of votes can be pulished.
If the Group creator "Banned" a Group member, it has no effect and the banned member can still share stories to that Group. The banned member's profile shows he's still joined in that group.
If the Group creator edit the member to become Admin or Moderator, the edited member still doesn't have permissions as an Admin or moderator.
The Group creator can even banned himself and still he's the Admin of that group. IMO, the original Group creator should not be able to banned himself or set it's role to just Normal & Moderator.