Direct answer
Objectives follow journal display order. Some depend on your choices; follow the active objective in the game.
Result
Ducal guardsmen commanded by Captain Damien de la Tour were to aid Geralt in storming Dun Tynne - this was the duchess' wish and command. The briefing before the assault would be held at the mill where Dettlaff had recently dispatched Count de la Croix in cold blood.
