Each group has an "owner", who is also an admin when creating the group. They can assign any number of members to become admins. Admins have the ability to remove members from a group, but they cannot remove other admins, only the owner can remove an admin. When a member is removed, their content remains and can be removed piecemeal. Please reach out to firstname.lastname@example.org if all the content of a member needs to be removed from a group.