Just to say again, I have seen FOF folks held at gunpoint with a person talking. They were shot repeatedly before they could get a shot off.
Maybe someone thinks they are hot stuff but I suggest you try this before you opine that you won't be shot.
Also, even if you shoot - you seem to have the opinion that your shot is instantly disabling - don't count on it.
Also, I might remind you that some folks are taught that when holding a person at gun point and threatened - shoot the person in front of you immediately and whirl to engage the other as they will be standing there with their mouth opinion - unless well trained.
Someone has also mentioned backup - crooks and cops might have it. Again, in FOF, when the gunfight starts - you say: Why, O dear I have commandoed this dude and now someone else is shooting me.
Ok- in a convenience store robbery - I'm in line in back of a BG shooter. He shoots the clerk. I draw and take him down and tell him not to move. I'm drawn on by his backup. I shoot him (as he is talking). General gunfight continues.
I think there is a touch too much of assuming the plan goes your way when you take out the gun. It might but in this one, I return to the verbal challenge approach. That will distract the ambiguous gun dude. If he is a real bad guy, brother can do the Chuck Norris on him or flee. It will be disambiguated. Of course, if unknown to you, your brother is a criminal, then the cop will be mad at you. Don't count on your brother to come back for you.