Two sisters.

That's exactly what's bad about it. Even from a realistic point of view, it doesn't make sense, let alone in the context of the game. Your task was a quick attack – a full-scale invasion, but the mission was designed only to make you hurry and clear your entire territory and gather troops by a specific deadline. Then it becomes clear why the dwarves managed to gather. Although, again, I don't fully understand Rolf's actions yet.