Removing members tab from the navigation (top bar and navigation portlet):

• Log in to Plone as the admin user.
• Navigate INTO the Members folder (you should then see folders for the other users).
• Click the Properties tab (next to Edit and Sharing)
• Under where it says Allow Discussion there should be a tick box called 'Exclude from navigation.
• Tick it and Save.

Remove anonymous access to the members folder (even if its hidden):

• Go into ZMI to the Members folder
• Click the Security tab
• Scroll all the way down to 'View' in one of the last 'Acquire' sections and untick Acquire
• Untick the Anonymous box further to the right
• Save the changes.