I don't like to change targets, I just cast on who I need to. So for healing, I use:
/cast [target=focus-target, help] HealSpell
/cast [target=focus-target-target] HealSpell
The first one is so I can pick who to heal or heal someone outside my party (BG, etc). The next one is heal whoever has aggro. I like that since even if a pet, a alt, a anything pulls aggro, I can heal them.

Just my thoughts on your team. I am defensive player, so I might not burst people down, but I try to almost never die. I would put down a healing stream totem. It is easy, simple and auto-magic. You can get it at 20 through shammy quest. Yeah, it takes forever to get, but worth it. I would use holy nova for AOE healing. You can get a glyph that makes it stronger for heals. I can't really suggest judgement of light, since you have all casters and wisdom will help more. But later when you get seal of light, I would use that since it should mean less heals needed for the tank. I also love food. Cheap, easy, don't need reagants anymore and gives stam/spi. The stam means that the alts have free health so you should have to heal them less (in theory). Also, it is messy, but holy light has a glyph that heals 5 people for 20%. Sure the tank shouldn't heal, but for super lower areas <40, it probably won't be too bad since can only delay casting 2 times (2 hits) and it is just until you get chain heal (I think 40 or so). Hope that helps and good luck.