You can probably do that by setting up stopmacros for the characters

Shaman 1:
#showtooltip
/cast [nomodifier] Lightning Bolt {Or whatever your normal 1 key is]
/stopmacro [modifier:alt]
/cast [modifier:shift] Tremor Totem

#showtooltip
/cast [nomodifier] Chain Lightning
/stopmacro [modifier:alt]
/cast [modifier:shift] Earthbind Totem


Shaman 2:
#showtooltip
/cast [nomodifier] Lightning Bolt
/stopmacro [modifier:shift]
/cast [modifier:alt] Tremor Totem

#showtooltip
/cast [nomodifier] Chain Lightning
/stopmacro [modifier:shift]
/cast [modifier:alt] Earthbind Totem


Pressing 1 will Lightning Bolt for both.
Pressing 2 will Chain Lightning for both.
Shift-1 will cast Tremor Totem for Shaman 1.
Alt-1 will cast Tremor Totem for Shaman 2.
Shift-2 will cast Earthbind Totem for Shaman 1.
Alt-2 will cast Earthbind Totem for Shaman 2.

I hope this helps.


Edit: I also have a few questions and I don't really feel up to making my own thread. <.<

1) Anyway to macro "Stop Following" or just "Stop"? Currently working on a Ret Paladin/Shadow Priest setup and that would be oh so handy to get the ball rolling with the priest before my paladin gets to its target.
I would use the multiboxing addon to have the priest follow once combat ends.

2) Any better method for beginning the quest turn in process than having to right click the quest giver on each character? Once the dialogue box is open, it is easy enough to turn in the quest with one character.

3) I can tell early on that I'm going to run out of room for macros. Are we still bound to only having 36 macros (18 per character, 18 for the account)?

4) Going back to the first question, is it even worth the hassle of dualboxing a melee and a caster?