How do people heal during fights?

I have paladin, h priest, s priest, warlock mage.

I currently run a macro which stopcasting, either healers target's friendly focus OR targets focus's enemy's target and heals.

Since I been one shotting everything with 4 casters as one, I haven't needed to heal much .. but I'm finding it a bit annoying if different targets get hit. Then if I want to heal targets then, I need to target with paladin, which means he's not tanking.. blah blah..

Do people prefer to setup a healing macro for each member of the party? or is there any genius ways of doing this?

Is there an addon which checks the health of party members, round robin in a priority order and casts a heal based on life left? like 90%+ = renew, 70%+ = flash, 40%+ = gh, 20%+ = shield

Then once shielded heal... or something ... is that even possible?