tmux new-session -d -s userone-internal
tmux new-session -d -s usertwo-internal

tmux new-session -d -s userone
sleep 0.05
tmux send-keys -t userone "TMUX=''" C-m
tmux send-keys -t userone "tmux attach -t usertwo-internal" C-m
tmux split-pane -t userone -h
sleep 0.05
tmux send-keys -t userone "TMUX=''" C-m
tmux send-keys -t userone "tmux attach -t userone-internal" C-m

tmux new-session -d -s usertwo
sleep 0.05
tmux send-keys -t usertwo "TMUX=''" C-m
tmux send-keys -t usertwo "tmux attach -t userone-internal" C-m
tmux split-pane -t usertwo -h
sleep 0.05
tmux send-keys -t usertwo "TMUX=''" C-m
tmux send-keys -t usertwo "tmux attach -t usertwo-internal" C-m