Strive to have, at bare minimum, Adlo on tank before Death Sentence. From phase 2 (conflags) onward, always have a Lustrate ready to go the moment you see the hit visually connect (precasting Adlo or Physick also helps). You'll only be able to have Virus on every 2nd or 3rd one, so chances are your tank will have to eat a few with only their own mitigation, Adlo, and maybe Stoneskin.

Have Succor on the party before each fireball.

Your strategy for tanking snakes will probably vary, but it's pretty vital to be able to get off at least 1 heal at your start and endpoints while you're dodging divebombs, and not succumb to panic/nerves by not healing tank at all. IE, moving just before your casts finish and still having it go off. You'll know what I mean when you get there.

I would recommend Eos for the fight; I used Selene for my group's first 4 kills, but starting with Twister phase everyone is too spread out to really receive her buffs, so I found Eos to be slightly better. You can of course fairy swap at that point if you really want to, but I'd rather just have the MP saved. You shouldn't "need" Selene's slight DPS boost to clear anything before that point.