To Alise:

I don't see how's that suppose to be almost impossible (95% as you said), DS Infirmity can be overcome (albeit not as easily!!) by timing your Cure II to land the moment DS damage takes place, but before Infirmity is applied (Hint: Start casting when DS cast bar is 55~60%).

Since we're talking two WHMs, they can alternate Divine Seal for each Death Sentence, so... assuming 1650 base Cure II heal value, 1650 + (1650*1.3) = 3795 HP has been healed, should be enough to weather any AA/Plummet that may kill your tank .