Each copy of WOW just has to be in its own directory.... as such...

you can do what I am doing. I have three windows in a triangle arrangement. The top screen is my main character and that window is slightly larger than the other two - in fact it overlaps them significantly.

Even with FFA loot if there is an item for a quest that needs to be looted the corpse will still glow for the other toons. As I can see enough of their sessions its easy to move the mouse, loot, and resume playing.