Tbh just stoneskin/adlo the Death Sentences and you take a nice chunk out.

We do Twintania with one tank, (PLD obviously) and it works out well.

I drop Soil when I can bunch it togeather with a Fireball and a Death Sentence, Succor before fireball ofc. Soil when snakes are all on tank and on last phase to simply reduce dmg for a while.

Lustrate to counter Death Sentence debuff when needed, if you spam Physick and the tank had Adlo/Skin up you should be able to keep a stack though, or just use it if you can use Aetherflow again, no point in wasting it.

Eos should be within tanks range for all the fight to help, the Rouse/Fey Illum/Whispering Dawn Macro comes in handy for some extra healing.

Last phase is your easy one, just do one Adlo, one Physick and repeat.

Get the SCH's crit up! I got lucky last week and Adlo was critting before nearly all the Death Sentences. Thats a shield for 2200 to 3700 depending if you have Fey Illum on yourself and tank has Convalescence up.