You need to, open full mission builder, set the mistel Ju88 at what ever altitude you want, accross two waypoints. Then get the Fw-190 A8 Mistel and have that fly at the same speed, same alt on a close parallel path, two waypoints. at every waypoint of the FW-190 click on the "set" tab at the bottom of waypoint and click on the mistels waypoint, for each waypoint. Then click player for the FW-190 and fly. there are tutorials on this if you look.