Revisiting: "Can the Captain FORCE/INSTRUCT/TELL/COMMAND another crew member to go into discretion???".
In Hong Kong where the ANO is an annex of the Civil Aviation Ordianance, it states that it's not permissable to force someone to work when they are fatigued. So if a crewmember tells the commander they are tired and he/she tells them that they have to work, the commander is commiting a criminal act.