Make the proper permisions for the screen command
sudo chmod u+s $(which screen)
sudo chmod 755 /var/run/screen/
sudo rm -rf /var/run/screen/*
From <user_sharing_screen>
name the screen
upon initialization
screen -S <session_name>
from within an existing screen
C-a :sessionname <session_name>
make the screen multiuser
C-a :multiuser on
C-a :acladd <user_to_share_with>
From <user_to_share_with>
on the same system
screen -x <user_sharing_screen>/<session_name>