Ok, playing around with Healbot...

It allows you to set which spells are cast, by how you click on the unit bar.
So far I have Flash of Light (left click), Holy Light (right click) and Cleanse (alt, left-click).

Under the Healing tab it has something called Target Bar.
When grouped with my shammies, I can Control + Alt + Right Click to add any of them to "My Targets" which moves them to a "My-Targets" list.
Is this the feature which will allows me to see them, irregardless of which group they're in?
Or is that another feature?

Under the Skin1 tab, there are predefined skins for various group types.
I'm happy with how my group works in instances and questing, so I'm pretty much only interested in the "Alterac" skin. I'm fine with hiding the addon at other times.
With this pvp skin, it only shows toons who are in range and in need of heals.
Is there a way to force it to show toons, so I can ensure they're position is where I want them to be?
If I can, I'd like my Pally and Shammies to be in a fixed position, and then other players who may need heals or such to appear if they're within range and below maximum health.
I use my pally for targeting, and the shammies are on a target=targettarget system, so I could easily configure a click to target that frame, at which point my team could heal if I choose to go that route.