Two flyers start together on the platform, each holding onto one side of the bar. They depart together, swinging side-by-side.
Most commonly both flyers will do a One-Handed Departure (a mirror image of each other). So the left flyer has their right hand on the bar, the right flyer has their left hand on the bar (both around the middle). Then they jump together and both put their other hand onto the bar.
You can find out more about this trick in my books: