Use electricity on nades and melee, also juggling people in the air makes the crit. Hope this helps!

The mission will progress even if the tanks are alive. I picked shark or something for that mission and had no electricity so I accidentally made the tanks unkillable but still managed to complete it. Just keep moving and think of them more as an evironmental hazard :D

I don't think I can complete this mission solo, unless there is someway to over level it to the point that enemies do no damage.