Share Session with Two Different Users
Client User being loislane initiates the tmux session,
tmux -S /tmp/tmux-loislane attach -t shared
This will create a file which tmux refers to as a socket for connecting called tmp/tmux-loislane and only usable by Lois. Next Lois decides to give Clark access. He relays to her his user name clarkkent. Using ACLs Lois grants Clark access,
setfacl -m u:tinpham:rw /tmp/tmux-loislane
Clark on his console then connects to the socket file,
tmux -S /tmp/tmux-loislane attach -t shared
The result will be that both Clark will see Lois' session and also be able to type in it too.
Disconnecting Properly from a Session
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Reattaching to a Session
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Research
Solution at bottom takes group approach to tmux - http://www.linuxonline.ca/?q=node/397
Good intro - http://www.linuxonline.ca/?q=node/397
Another good intro with some background - http://spin.atomicobject.com/2012/01/28/less-perplexing-terminal-multiplexing-with-tmux/