Scripts

Because, according to the condition (else), if the object (city?) "castle" does not belong to player 2, then the video is played.

If you need it to play after capturing the city, you need to add a script for capturing the city with the activation of a function through OBJECT_CAPTURE_TRIGGER, where we check that the city has been captured and who the new owner is, and then we will play the video if the city was taken by the player who owns the hero you need. Something like this:

function TownCaptured( oldowner, newowner )
      if IsHeroAlive("Hafad") then
            if IsHeroAlive("Christian") then
                  if ( newowner == GetObjectOwner("Christian") ) then
                       StartDialogScene("/DialogScenes/FallenKnight/S3/DialogScene.xdb#xpointer(/DialogScene)")
	               sleep(1)
	               SetObjectiveState("prim5", OBJECTIVE_COMPLETED, 1)
	               SetObjectiveState("prim6", OBJECTIVE_ACTIVE, 1)
	          elseif newowner == PLAYER_2  then
	               SetObjectiveState("prim5", OBJECTIVE_FAILED, 1)
	               sleep(10)
	               loose() 
                  end
            end
      end
end 

Trigger( OBJECT_CAPTURE_TRIGGER, "castle", "TownCaptured" );

Thus, after MoveHero from the function with the hero's respawn, the conditions and actions can be removed)