Very few schools actually address "multiple-opponents" in any sort of actual training manner. Lip service at best.
http://www.army.mil/usapa/doctrine/Active_FM.html
I think 21-150 is the unarmed combat manual with probably the best lined-out tactics for multiple-opponent training that you can find on the net.
Some decent videos and chat can be found on the systema/rma websites and lots of stuff at Demi barbitos place (and links too i think..)
www.demibarbito.com
I doubt that any of us train multiple opponents with any frequency.