My first group was mid 220s in terms of ilevel when we cleared. Our composition was DRK, WAR, WHM, SCH, MNK, DRG, MCH, and BLM. My second group was around ilevel 225-230 with a composition of DRK, WAR, WHM, SCH, NIN, DRG, MCH, SMN when we cleared.

It sounds to me like tanks aren't cycling cooldowns properly or heals are struggling to keep up... or possibly a bit of both. The busters and balls do quite a bit of damage, so it's pretty important to have them topped off, even if they're just missing around 10-15% of their HP. Shields on tanks are also pretty important for the busters and balls-- things like Adlo, Stoneskin if you can, etc. I haven't run this as AST/WHM, but I would imagine a Noct Stance AST's Aspected Benefic could help quite a bit with it.

As a WHM, since I've run it more as that than as SCH, I am usually the one baiting the Double Drill middle, and toss out things such as Medica II when it's needed. I usually save Tetra for emergencies, like if there is a Single Drill and someone is looking particularly low on HP or a tank buster/tank orb is incoming and a tank is needing a quick heal. I try to keep Stoneskin on the tanks as much as I can, but usually when the AoE orbs hit, I leave the shielding for tanks to the SCH and focus on topping everyone up. I don't have a tank cooldown rotation from my tanks available at the moment.