The main team caller is normally the medic, because they know how far they are from uber and should be the most aware of their surroundings. The whole team hinges around the medic so it makes sense to have them calling the shots. The two scouts should be working together as you said to scout out the opposing team, and report as much information back to the rest of the team as possible, and attempt to get any pickoffs they can. A scout for medic/demo is a very worthy trade.