I'm in the exact same boat as you!
My boyfriend (Chaosomega) has 3 shammys as DPS and so i took the role of tanking and healing. (paladin and druid)

It's actually easy to macro and not that difficult to do. Although it's not a syncronized as DPSing, but it works. Just have druid on follow, and before every pull keybind a key (for me it's "t") which makes my druid strafe to the left, therefore breaking follow. I had my druid's moves on 12345 and my paladin's on 67890-=.

I use a modifier macro which allows me to put 3 moves on one macro for my druid:
/target party1 (or whatever)
/cast [modifier:cntrl] Regrowth, [modifier:shift] Rejuvenation, [modifier:alt] Healing Touch,
/castrandom Swiftmend

but putting this macro on 1-5, i can heal the whole party. Just remember that whoever is leader is party1, and the healer (in my case my druid) is always party5.

So as my druid sits back and heals constantly, I am usually focused on my paladin's screen, tanking.
I haven't really found a good way to keep track of all the seals and judgements but the main moves i use are consecrate, avenger's shield, hammer of wrath (I think its called) and righteous defense. So, like every good tank, just spam those buttons and you'll be good to go.

Also, have a macro that makes your healer /focus the tank. And at the end of every battle make a macro /follow Focus and keybind it somewhere useful (i use the ` button) so you wont leave your healer behind.

BTW the /castrandom swiftmend is a druid move that consumes a HOT and heals the target the full amount instead. This is useful because say i cast a rejuvenation on my paladin but she's dying too fast. I then just press the button 1 again (if the macro on one is /target paladin) and it automatically casts swiftmend without having to press ctrl, alt or shift.

Just some useful tips for tanking and healing good luck

Chi