I focus my main. Then my alts use:
/cast [target=focus-target] DPSSpell for DPS
/cast [target=focus-target-target] HealSpell for healing
It ends up damaging whoever the main has targeted and healing whoever has aggro from the mob that the main has targeted.

You can use castsequence and dummy commands to make only 1 spell at a time.
(alt 1) /castsequence [target=focus-target] reset=7 Earth Shock, , , , , , , , , ,
(alt 2) /castsequence [target=focus-target] reset=7 , Earth Shock, , , , , , , , ,
(alt 3) /castsequence [target=focus-target] reset=7 , , Earth Shock, , , , , , , ,
etc

I will just skip to the end, and you can leave out the parts you don't have yet. I have 3 resto, 2 melee. I put them down in schools (fire last, since it might pull a mob).
/castsequence reset=combat/16 Stoneclaw Totem, Healing Stream Totem, Grounding Totem, Searing Totem (for resto's with 1 using mana spring instead of healing stream)
/castsequence reset=combat/16 Strength of Earth Totem, Healing Stream Totem, Grace of Air Totem, Searing Totem (for 1 melee)
/castsequence reset=combat/16 Stoneskin Totem, Healing Stream Totem, Grounding Totem, Searing Totem

Then I put searing, grounding(1 grace of air), healing (1 mana) on my broadcast list so I can lay 5 down at once. I mean I put all chars have searing on F5, so I can push F5 and get 5 searings.

Just use /follow on the alts to follow the main. If they get really behind (you can see in mini-map), then just slow down a sec and let them catch up.

Is there a particular reason to spread out? If you need to target someone, you can just click on their portrait in the party area.

Hope that helps.