IF you are using IS you should set up those click region things to click heal with the priest, unless you are running the priest as main, then you can just get clique and heal away, and if you'd rather use keybindings (like I do with keyclone) just make a keybind for healing each character with the macros targeting by name.
As for that fight, be sure to run out of fires on the ground, and be careful with the breath of the dragon. That's about it.