did you install Cookies toolkit? The logout function requires cookies toolkit to be installed.
after you install cookies toolkit add the Clear Session Variables behavior. Open the server behaviors panel, click the plus button, and select WA Cookies -> Clear Session Variable.
set the trigger to before page load, and set it to clear all sessions.
for the members, don't create a separate table. use the same table, but use User Level authentication to give different access rights to different users.
see the User Level Authentication tutorial on the Archived Documentation section of the security assist support page.