I assume you are killing the "pods" that spawn in the Dagrin fight before they become Magmatic. If you are not, then that is a certain fail condition.
Initially, I tried pulling my group to the pods to kill them. They spawn over a very wide area, so you need to use the radar to see the pods so you know where to run. After a while I got tired of this because its a huge pain, so I wrote a script to send my Dirge after them. This makes that fight much easier - you just camp your group, pull Dagrin to them, turn his back to them, and tank and spank. The only thing you have to be on top of is the flames effect he spawns (didn't pay attention to the name) because it will knock the tank back quite a ways if you don't attempt to mitigate it. Its easy to mitigate, however, because you can place the tank underneath Dagrin and fairly far rearward and he will maintain his position facing you. When the flames spawn, just push forward a bit, and the knockback will be small enough that Dagrin will not move.
That said, you still need a very tank-spec'ed tank and a very heal/debuff-spec'ed healing team to get through this, as well as all other fights in this zone (I use two healers, although I think I could get away with one now.)
As regards Getiar, the key to this fight is having at least one mage in your group to cure the "Glacier Smash" effect that renders all beneficial spells inoperative - your tank will likely die if this is not immediately cured. I use a coercer and use the Priority tab to cast "Cure Magic" on my Inquisitor, Defiler, and Tank. Once you get that going, then its very similar to the Ahrmatal fight - use a MA, have it target the add/target the named. When you enter the zone, the first slab you come to is where I camp the group, placing them at the end nearest Getiar. I then preward and pull, running the tank to the the opposite end of the slab, and he always stops just a little past the group. Getiar will port you short distances around this slab, but its not problem and he never moves off his perch; you just have to run the tank back into position (TBH, once your tank can survive the hits, you could probably campspot the tank and AFK it).
And, if you have a coercer, there is another thing you can do that can greatly improve your ability to get through the occasional tank one-shot by keeping the mob away from the group until the tank can get back up. I will leave it to you to figure this out (its not too difficult if understand coercer abilities)