We need to keep them away from each other for obvious reasons. Despite their shared HP total, our debuffs tend to only affect one target, which means we still need a focus fire target.
The intended strategy seems to be focusing on Lokradin while trying to keep Thorai where he is for one or two rounds. Accomplishing this with immediate/opportunity actions could be difficult, since Thorai can daze. Assuming we would need other resources to keep him at bay anyway, we may as well stay out of his reach and not offer Torinn as a target. The room happens to be wide enough for even a 10-square ranged pull to potentially fall short, but really, Samel is already in range. It won't be easy to stay away.
As an alternative, we can focus fire Thorai instead. With Samel's debuffs, high Soldier defenses become irrelevant. Thorai also seems to lean toward single-target attacking, which should make crowding around him a bit less dangerous. His only AoE attack seems to be his clost blast 3 hammer attack, which shouldn't target more than one party member as long as we position ourselves properly. Also, since Lokradin may be content to stay where he is for a round, this method could buy us extra time.
For either option, because we lack powers to immobilize/restrain, a prone + daze will have to suffice.
Channel the Leyline remains the biggest mystery. So far, they've been area burst 1 powers that also create zones, right? A completely random guess: maybe this one inflicts a vulnerability to their attacks? Any thoughts?
Lastly, Myn's Crown of Stars gives him a lot of weak minor action attacks, which seem well-suited for clearing mutated scarab minions.
Specific tactical suggestions are welcome, especially if they take into account pillars and scarabs and whatnot.
this is not a definitive plan or anything
i couldnt be here to discuss these ideas w/ you guys yesterday so im hoping this can spark a proper strat discussion