If you are wiping at 2-3% , kill Toth first as his soft enrage is not so good. At roughly 5% or so , switch dps and kill Toth , and then heal through Zorn's soft enrage. By the time you get Toth down you should have 4-5% on Zorn which is like 36-45 k health( and that is not a lot ).
Not sure it will work 100% for you though as everything matters, healers, dps, tanks, etc., but practice makes perfect.
Good Luck!