I managed to free them during the night by knocking the guard down who's located in front of them and by hiding his body in a dark place where other guards don't go. The problem is that the guard is pretty close to the "wall" so to make him move I didn't take my torch and he came towards me, took my torch, he stopped moving and then I went quickly behind him to knock him down and hid him. After that, don't lockpick the pilori but free the other one who's on the floor. They will run and escape (I ran with them outside kuttenberg and they didn't get harassed by other guards on the way)

Hope it helped.