First, you have too much overlapping buffs in your current setup.
Second, you need more than one shammy for fully utilizing totem buffs. For example, you will often need Stoneskin and Tremor totems, WoA and Nature resist, ToW and Frost resist, etc. So if you get resto and elem shaman with DK tank, you won't need warlock and boomkin. I highly recommend to get a priest, fort buff is the most important buff for multiboxing, and shadowpriest's aoe does not need to be mouse-targeted.
So for you I'd say the following option: DK, elem sham, resto sham, spriest, mage. You can sub mage for boomkin if you want to trade free water + AI + ports for battlerez + 3% spellhaste. It will also allow you to distribute gear a bit better.