my suggestion would be to remove the warrior and use the pally as the tank. My reason for swapping out the warrior over the pally is the way the pally can tank multiple mobs at the same time and build agro while doing so. It makes life as a multi boxer easy.

add a shaman in the group for totems (buffs like windfury) and add the warlock and you should be good to go :}. The only down side to your setup is the fact that you have so many different classes it will take a lot of keybinds and macros to make all 5 classes work correctly.