Maz, if you use keyclone, just enable the PiP functionality in there, bind each region to a different key (again, I use F6-10 just for ease) along with this macro

/focus [target=tankname,help,nodead]; [target=secondname,help,nodead]; [target=Thirdname,help,nodead]; [target=Fourthname,help,nodead]; [target=Fithname,help,nodead]

and use bongo's (or your keymapper) to assign that macro to all the keys you have set in keyclone for your PiP regions.

Now, when your main character dies you will just need to hit the Function key that corresponds to your next most tanking character and their screen will pop onto your main monitor using the PiP functionality and the focus for all your other characters will be set to your second name character through the use of the macro, and so on down the list until you are all dead

Doing this works fine for me, but it does require mouse-driving rather than using keys, because of the issue you outlined of movement getting screwed up if all clients use the same movement keys so you may have to get proficient in it if you aren't already but other than that I find this setup is fine...I just am still not quick enough with it in arena's so once Smara goes down I just ignore the screens until I need to exit the arena