>What I understand and know:
>- 2 instance of the same browser on the same machine = 2 tabs in the same browser = same cookie
>
>- login on another browser / same machine or same browser / other machine > different cookie > new session > user ID from application (lookup in a table) > kill other sessions using this app user ID and another session ID

Yes, for that part, all is ok. It is the first one mentioned here that I am trying to deal with.