Healing Ultima is intense.

[Tinks]

But thus far, there's really only 1 problem that I haven't see any good solution without consciously preempt for it:
In one of the DF run, the eruptions were chasing BOTH healers...ended up no one healing the tank and eventually resulted in a wipe.
I wasn't prepared for that, so Benediction and Swiftcast already used-up prior to this stage.

With 2 healers, in theory one of them should have lustrate, swiftcast, or benediction available between them. I've been in those parties where you can't rely on your other healer to get the job done, but this is one of those fights where you need both healers on the ball until everyone is dodging well. It might be that you need to macro swiftcast and discuss when you're using it with the other healer.

My only other suggestion, is divine seal + regen. It might buy you enough time and you can do it while running. Last resort, eat the eruption, cure the tank, and let the other healer raise you if you die.