A pally and four shammies is a pretty decent group.
I would dual spec one of the shammies.
That gets you either Pally + 4x Elemental or Pally + 1x Resto + 3x Elemental.
You might want the Resto vs challenging content, and the Elemental vs farm/trash etc.

Ensure your pally uses a proper 96969 macro, as that makes everything so much easier.
Basically, put 1 point into Judgements (reduced cooldowns) and do not glyph Consecrate.
Then you pick 1 of Holy Shield, Judgement of Choice and Consecrate as the first 9.
A different one as the 2nd 9. The remaining one as the third 9.
The final macro will be two strings of 96969 - 69696.
For the 6's, just alternate Shield of Righteousness and Hammer of the Righteous.

I like to have Consecrate as my 3rd 9, so I have the option to manually hit Consecrate and it will be ready again by the time the macro calls it.
If you spam the macro, your Holy Shield never falls, and you're using each ability just as it comes off of cooldown.
Have the pally talent which refreshes Divine Plea on a melee hit, and use it before larger pulls.
Pallies are amazing boxed tanks.

Shammies should go with a click castsequence, on the same keybind as the 96969 macro.
With a forum search, you'll find a decent one, or look up Fursphere's Macro thread.
I have all shammies to Lesser Healing Wave on key 4, and all shammies Chain Heal on key 9.

Then have dedicated heals for the Resto only.
Lesser Healing Wave, Healing Wave, Chain Heal, Riptide and Earth Shield.
If the tank was pummeled really hard, the elementals can assist a bit in heals.
But for the most part, a dedicated healer can handle whatever, while the dps just dps's.