We tried it at 39 but failed. We tried it again at 42 and this time it worked. You can have the healer step off and heal the remaining 3 on turrets but we just all stayed on the turrets. As long one person is alive when all the colicoids spawn you wil get past the encounter.
Also aim for ranged droids first or they will take you down fast.
You can see a video of our attempt here as well as the rest of the flashpoint.