Grounded Drakelings can be rooted, Unfocused Drakelings can be mesmerized, Confused Drakelings can be charmed, and Twisted Drakelings cannot be affected by crowd control.
We would always immediately kill the twisted first, and have bards charm any confused, while enchanters mez any unfocused, and off tank the grounded. Have a ranger vinelash the grounded. You must hit each drake with their CC weakness to get the achievement, and this includes the 3 drakes that spawn when the Ancient Dragon hits 0%.