If you require a squad member's ability (i.e. you need an engineer to repair a junction box to open a door so that you can progress further) but their trust in you is too low, here's a last-ditch desperation trick you can use. This is not suggested until you've tried healing them and/or giving them a gun or ammunition.
Go into first-person mode while standing near the squad member and aim your gun at their head. Keep your sights on them for three seconds or so, and the game will cut to a scene of the squad member reluctantly complying to do your dirty work. Afterward, it should cut back to a screen giving you the option to have them perform the task. However, their trust will drop significantly, and if anyone sees you threaten them, their trust will drop as well. This tactic should only be used if you are absolutely at your last resort, because if the coerced person's trust drops too low, they will turn on you in a hearbeat.
Defeating Boss 3:
After the cut scene, get under the boss and notice that it won't hit you. If it does, move around a bit until it stops hitting you. Shoot it until it's in the red. Stay in your spot, turn to the walker in the tank and shoot that until it's in the red as well. Then flame it or use flame grenades until it's dead and shoot the scuttlers. Now concentrate on the boss by courching and flaming it. It shouldn't take long.
Thanks to Revolution reader "Double H" Hunter Hendricks, Mossamur, naveah, Scott McCutchen, and TJ!