Every phase:
HEALERS ALWAYS PUT TWINTANIA ON FOCUS TARGET. Not just for twisters, also for death sentence during the first 50%.
WHM:
Death sentence is every 35 seconds. Make a macro that counts to 32 seconds then gives you an echo warning in the chatbox or something and hit the macro when death sentence hits the tank. Then when the macro hits 32 seconds and warns you you start casting stoneskin. If the stoneskin is applied before TT starts the Death Sentence cast the tank will end up with 18% more health after the hit which is huge. After stoneskin is up death sentence should be beginning to cast, this is where you start casting Cure 2 on the tank. The cure 2 will hit the tank right as the Death Sentence hit and recover a lot of lost health so the tank won't die to autoattack/plummet after.
SCH:
You can have Sacred Soil and Adloquim up for every death sentence easily, as well as having enough stacks for lustrates.
Sacred soil has a 30 second cooldown so it lines up perfectly with death sentence. Pay attention and drop a sacred soil while the first Death Sentence is casting. Then every time it comes off cooldown cast a Physick/Succor depending on what's needed to pass 2.5 seconds, then drop a new sacred soil. After dropping the new soil start casting Adloquim on the tank. When you do this the tank will gain Galvanice before death sentence hits and take much less damage. You should have enough eatherflows to lustrate the tank when death sentence hits even if you use a sacred soil on each one.
The SCH can also call out death sentence after sacred soil comes back available to let the WHM when to stoneskin, instead of the WHM using a macro.
If the tank is using a cooldown, and the healers are using Virus when the tank has no cooldowns left, death sentence will never hit for more than 3k if the healers are doing their job properly. One lustrate and the cure 2 hitting means the tank should be well and good into the safe health range.
Proper Death Sentence healing, following these guidelines, means the tank will never be even close to dying.
Phase 2:
WHM: When fireball marker appears hit Surecast and then cast medica 2, no matter what group it's on. It will heal everyone to full. There is no death sentence when TT is casting fireball so it's easy to get a medica 2 in. If the fireball is on your group you will be interrupted without surecast so always have surecast up for it. If you messed up and didn't start casting before the fireball hit, then swiftcast the medica2 as a backup plan, but it's not ideal because you still have to wait for the GCD after.
SCH: Putting up succor before fireball hits people is a good way to make sure they don't drop too low. This matters the most right before the fast conflags because someone might be low from fireball and get put in conflag right away, so the higher they are after the fireball the better. Throw out another succor after the fireball hits if possible.
Divebomb phase:
both: After you dodge the divebombs, you have a full 2.5 seconds to cast a heal on the tank before having to go back to stack with the rest of the group. You can heal just fine while dodging so do so or the tank will drop too low. Save lustrates and sacred soil for when all 5 snakes are up. Keep eye for an eye on the tank that will take the most damage.
WHM: Don't use benediction after the 2nd set of snakes spawn. JUST DON'T
SCH: Put the pet near where the tanks will be. This will make the pet not get hit by divebombs and also make them help with healing. Don't forget the heel the pet quickly after the 2nd set of divebombs, you'll need the extra healing. Use the pet's cooldowns when all 5 snakes are up. Aim your sacred soil on top of the tanks picking up the snakes, this helps the caster aim their limit break too.
Twister Twister Twister
both: when TT comes down to cast the Aetheric Profusion(ultimate attack) have virus on her and sacred soil on the group. Pre-cast aoe heals even though you're in the neurolink to get people back up asap after the damage hits.
WHM: Heal extra hard when dreadknight comes down in case a healer gets imprisoned. If you have a BLM on the task of putting Heavy on the Dreadknights and the BLM gets imprisoned, tab to the dreadknight and cast a Stone 1 on it after topping off the tank. Keep doing the same thing as before for Death Sentence.
SCH: When Dreadknight comes down put an Adloquim on the tank and then quickly tab to the Dreadknight and cast a Miasma on it to slow it with disease, then continue healing the tank. Lustrate might be useful after using a GCD to put up miasma but usually isn't needed unless the other healer got imprisoned at the same time. Keep doing the same thing as before for Death Sentence.
Phase 5
both: Easiest Phase. Just do the same thing as always for death sentence. When TT is casting Liquid Hells, nobody except the person targeted by it will take much damage, so throw a heal on them. Use healing cooldowns when tanks get targeted by Liquid Hells. Coordinate cooldowns with tanks if they get targeted by Liquid Hells repeatedly due to lolRNG. Offer a sacrificial virgin to the RNG gods for your Allagan weapon ^^. If you did the rest of the fight properly this phase should be super easy no matter how bad your RNG is.
For a more in-depth guide for every role on this fight, check out the excellent Turn 5 guide by ShinRa.
http://shinra-ffxiv.guildwork.com/fo...e-shinra-style
It's the most detailed guide on the fight out there.
SCH is by far the strongest/easier heal class between the two, on this fight. Yes the SCH has 3x more to do as the WHM is mostly just spamming heals because the SCH also has to manage aetherflows and micro the pet, but as a SCH you are way more suited to keep the tank alive no matter what happens to the WHM. A good SCH makes this fight a cakewalk, a bad SCH makes this fight a nightmare.
Final suggestion: if you have a skilled SCH and a skilled Tank with good gear(easy with 450 myth per week) then doing this fight with 1 tank and 5 DPS is much easier than doing it with 2 tanks. Just make sure the Tank and healers aren't scrubs and you'll breeze through it with 5 DPS, you will never have to worry about not killing conflags or snakes or dreadknights in time if you have 5 DPS making the fight much easier overall. But again, you need good healers and a good tank to do it this way.