When you use the Video Screen PIO it shows two different weight fields, one for the screen and one for the PJ, which leads me to believe you should be able to attach the screen as a load on one truss and the PJ as a load on another. In reality, I have haven't been able to get this to happen. It all assigns as one item (as far as I can tell) so I've added load items for now. Should they be attachable separately? Or is that something that is in the works?
Unfortunately for Vectorworks 2018 is planned to be able to attach only the video screen. If you need to include the projector properly in the calculations, you need to set it's location via the OIP parameters for Projector distance and vertical position. Note that Braceworks calculations don't need a Hanging Position, it's meant to allow hang with offset (via the Witness Lines) and also object associations. In the attached image no Hanging Position is used.