We did it. Kael'Thas is down. Congratulations to Fire and Blood!
I feel a bit proud of myself; some of my analysis really helped out. People did use their staves more and put that into a macro. We did end up taking melee off of Thaladred and putting it on Sanguinar. We also switched up the order we had been killing the advisors, having Sanguinar die second instead of Telonicus; this made a really big difference in P4 on killing the eggs and interrupting Kael, and Sanguinar seemed a lot more dangerous than Telonicus to the raid once we started using our staff correctly.
Something we tried that seemed to work better as well was not doing as much AoE. We switched to focus firing the weapons, and that actually seemed to take them down more quickly. I don't know why, either.
Tanking wise, I had a fairly easy job of it. I didn't tank a single advisor; my roles were to:
P1: be hit by Capernian's conflagration
P2: Tank devastation - usually lasted into P3
P3: make sure telonicus tank has staff debuff & dps telonicus/run weapons as I can
P4/P5: pick up phoenixes
The hardest part in there was tanking the phoenixes. Devastation doesn't do anything special; the only annoying part is to position him so that he takes AoE damage while not instagibbing the melee, but that's not so hard. The phoenixes are pretty interesting to tank though. They can spawn nearly anywhere. They need to be dragged from wherever they do spawn to somewhere near the melee but not on the melee, and they need to be dragged so that they aren't running through the healers. If another one spawns, that one needs to be tanked as well - and they can spawn while you're killing one. (I learned that the hard way on a p4 try, where a third phoenix was running rampant through the healers while I had 2 tanked. It didn't end up mattering, as I was mind controlled shortly afterwards, but it could have.) And they have a giant knockback effect when they die. Our strategy was to not waste any DPS on them while they were alive and quickly down them when they were dead. This seemed to work pretty well. The fire resist gear was great for this; I mitigated 63% of all the damage from the fire of the phoenix. Now, one can kite them with ranged DPS, but it seemed to work fairly well this way and it meant that our ranged DPS could focus on Kael instead of kiting. And clearly the positioning worked well too, as melee was easily doing twice as much damage as ranged on the eggs.
Now that I think of it, this would fall apart if I did get MCed. It was fortunate that I did not. When we do this fight again, we should make sure to have a backup plan in that case.