So the key thing to point out is the order you kill the adds does not really matter as long as you kill them quick. The easiest way to do the fight is actually using 1 tank, Tank picks up the ass from the west each time and the DPS burn the one from the east (normally bard tanks it) then burn the 2nd on on the Tank. Same method is easily used for 2 tanks just the off tank tanks the one from the east. This method keeps the adds on the outsides faced away from the group in most optimal positions.

When you have 2 tanks, with this method you can actually burn either add 1st and follow the green first if you want, but the tanks never need to worry about what they are picking up as they always get the same add, which 100% solves the color blind issue (assuming that at least one of the group isn't color blind). The other reason this method is also very nice is because for a lot of people only the line between garuda and one if the sisters shows up instantly (or sometime neither do instantly) and this allows the DPS to start dpsing the second they spawn (ranged dps) or get in range (melee) and results in faster sister kills.