i have 3 80 shamans and and a 3 frost DK team i have at lvl 77 now. I started my multiboxing in WOTLK with the shamans all elemental. I too experienced the problems you are having with melees when they get amongst your chars, particularly rogues.

Fast forward to cataclysm and i returned to wow and multiboxing and tried a melee set for the first time using the pseudo priority set up from Mogz DK video. I can tell you it's amazing and melee's are way easier to play. I respecced my shamans to enhancement and in many ways they are better than the DKs in BGs.

enhancement with wolves up every two minutes is incredibly fun. But most of all what i find with the melee teams is that you just do not have to worry about not facing the right way for spells or line of sight for spells and even when feared IWT will make your toons all run back to the target without having to worry about collecting them. If a rogue is stun locking on of your chars in the middle of the other ones IWT just makes your other melees turn and tear his face off before he can kill one of your chars.

And if he dies you jsut rez him, heal then are on your way to kill again without having the pesky run to the gy to pick up your resurrected character.

I'd never go all caster again after experience the ease of play i get with a melee team. But as others have said at that level your really sitting stationary duck for melee players to own.