I was having a super hard time with this also. I finally stripped Mako of all her gear and ripped the mods out of her gun and geared up Gault to try and burn one of them. Got 1 down on the second try and then the last guy was cake. Good luck.
I followed your advice on this after my first try, when I figured my tank spec wasn't going to cut it. Thanks for saving me a lot of grief and throwing things around my living room!