I still wipe on those guys occasionally in heroic, I absolutely detest them. They are hexable/stunnable/sheepable/etc, so you can use that to your advantage - hexing one while stunning/DPSing the other, using any undead fear/cc you may have (paladin tanks are good at this), etc. I have seperate strafe keys for my team and my tank, so I can usually strafe out before anyone dies but without enough HP (15k+) your guys will probably die. You may want to see if grounding totem does anything in patch 3.08 too, it didn't do anything last week though. You could also simply spread everyone out and let 1-2 people die while you take them out.

Alternatively one strat I did when I first started was zone out and reset instance if I saw double mage (lol). Obviously if you are farming the instance for XP/hour this is a bad idea, unless you are planning on clearing the whole thing which will take around an hour anyways.

Dunno if anti-magic zone would help out with a DK tank either, if you can pop that and have your guys hide in it while killing one quick. I would recommend using bloodlust on a double mage pull, you wanna burn em down asap. Plenty of trash after them for the Sated debuff to go away before Trollgore.