The weakest part of a Shaman was they had no good threat builders to tank. Back in vanilla I tanked every 60 dungeon just fine, as long as I didn't lose aggro. So each one is strong enough to take a beating and survive. Stacking certain totems and endless chain heals, you're fine.

Hardest part, imho is going to be able to gear them properly. I think as long as you have enough macros to cover each char (so it doesn't really matter who takes aggro) you should be just fine.