To get access to the special dresspheres you need to activate every node (node, not gate) on the current Garment Grid in one battle. Once you have transformed into each DS you can press L1 to get to the GG screen, then press R1 to change it to the Special DS screen. From here press X. Now the other 2 characters will leave the battlefield (I think you confused this with escaping) and the lone character will continue the fight. While in SDS you cannot escape, only transform back into a normal DS. When you do this the other characters will return and you can continue battling as usual.
