Am working on something like this but much much more extensive atm for 5 toons. But I'll give you a simplified version for your 3 spells are you dual boxing ? or 5? cos the setup changes somewhat with more toons :S

first things first

Your healing spell. You seem to always want that to target the toon itself rather then the main/brain.

for that I would bind "3" with:

/cast [target=player] Lesser healing Wave (leave "player" as it is.. don't change it for the character name)

put that macro on both characters in the same position.

Now I hope you are using Keyclone cos the next bit I've set up through keyclone and I have no idea how to do it otherwise.

Button 1 is going to be our main LB attack.
This is going to sound a little strange but you have to take your Lightning bolt spell from your spell book and place it where you have "1" keybound. No macros at this point. Do this on both characters.

Now create the following macros

on MrA:
/target [target=MrB,exists]
/assist
/cast [harm,nodead] Lightning Bolt

on MrB:
/target [target=MrA,exists]
/assist
/cast [harm,nodead Lightning Bolt

now bind that macro to say.. ctrl+alt+1

do the same with earth shock and bind them to 2 and ctrl+alt+2

remember the spell itself goes into the keybind you wish to use and the macro goes into a variation (i like using ctrl+alt or shift+ctrl+alt etc etc)

then open up keyclone and creat 2 new keymapping files:

MrA:
1 --> LBAT
ctrl+alt+1 --> LBBT
2 --> ESAT
ctrl+alt+2 --> ESBT

MrB:
1 --> LBBT
ctrl+alt+1 --> LBAT
2 --> ESBT
ctrl+alt+2 --> ESAT

the hotstrings I have listed above can be anything you want as long as they are the same for each toon.. I tent to go by a naming system like this:
Spell/Target. so "SpellA" means cast a spell on MrA.. "SpellAT" means cast a spell on MrA's target, SpellATT, means MrA's target target. SpellF means cast a spell on the Focus etc..
If you are unsure how they work, use the names i listed above for your toons

then once you made these two files, go to the command thingy in keyclone and make sure that you load the correct keymap file to each client.

what happens now is that depending on which client you have in the foreground, it will automatically send the other keybind to the other account and utilize the assist macros

so pressing 2 on ur current main, will send ctrl+alt+2 to your current alt.. as soon as you move over to your other toon.. it reverses and your new alt will assist your new main..

hope that's clear