Will they step up onto a perch if placed in front of them, if so you can start with that and slowly remove them from their cage, however don't push it, if they feel that their cage is their safe place then forcing them out will be a stressful event for them. If you open the cage door and sit by the cage and talk to them and maybe offer some millet at the door do they show any interest in it? When you adopt rescues you sometimes just have to accept them as they are, you usually don't know what their past experiences have been. One of my birds that I got from a rescue I don't think had ever flown before I got him, it was as if he did not even know how to fly. After he joined the rest of my flock he learned, but my point is that you just don't know their past so they may see their cage as the only safe place to be based on their past experience.