Stormonu
NeoGrognard
One other technique I've seen when one (or more than one) player is dictating the actions of another is to rule that any time you want to suggest of course of action to another player, you have to do it in-character. It's harder for someone to backseat drive when they have to do it in a way that their character can actually do, especially if their character isn't next to the "controlled" character and doesn't know all of the capabilities of the other PC.
Especially if it takes their character's action to perform said "backseat driving".