I am trying to identify a Sci-Fi movie from the 80s. Amongst the 'good guys', there are three identical aliens with a form of telepathy that allows them to synchronise their body movements. They have humanoid bodies, and glow white. They agree to an arm transplant and so an arm is surgically removed from one of the aliens. The arm is then sent as a gift to the bad guy, who transplants the arm as a sort of trophy. Once the arm is attached, or during the surgery, the trio of aliens try to control the arm (using telepathy from elsewhere in the galaxy) in an attempt to cut the bad guy's throat with his newly transplanted arm.