Once each drake/pack has been released, it gets controlled by Halfus and he gets 50% increased damage taken per one, so doing both packs means 100%.
The way we did it at least was to release the Nether Scion on the pull, and nuke that down (Tanking it on the boss for cleave damage of course). Once it was dead, we released the Emerald Whelp pack and tanked them on the boss and cleaved them down, while nuking the boss.
You should definitely kill both sets of adds, because then the boss will have 100% more damage taken and will be a lot easier on the enrage timer. Maybe when you outgear it severely you can just nuke it down, but for now at least that isn’t doable.
We popped bloodlust at around 40%, as you are able to stand still more towards the end of Phase 1 than in Phase 2.
This fight differs greatly depending on what add setup you have, so it's hard to write a step by step guide of what to do. It's basically a list of abilities.