Target all Probes first, confuse Spheres so they actually tractor the probes (lol).
My PUG group of 2 Tactical , 2 Eng , 1 Sci made it on the 2nd try. Basically what we did was to split up the group into 1 Tac/1 Eng for one gate and 1 Eng/1 Sci for the 2nd gate while me, the last Tac stayed near the portal to stop any probes left.
Try to take down the gates as quickly as possible because the spawn happens much quicker the longer you take. My team were still killing previous sphere spawns when another wave came in.
I used Emergency Power to Shields 1 and Reverse Shield Polarity for those extra seconds of life to kill probes. Doesn't matter if I died as long as no probes went through. Managed to destroy both gates at 3/6.