You have to be shooting to launch a grenade with left click...If You stop shooting left click moves the squad.

Cheers, I had finally worked it out :)

I have an additional issue: I'm playing on mac and the track pad simply doesn't allow you to do left and right clicks simultaneously.

On mac, while you're two finger clicking on the trackpad to shoot, hit left control button to throw grenades. Note that you'll have to upgrade grenades to increase distance, at first they're very short distance throws and can likely kill your squad.