Complex sentence: A vain emperor who cares about nothing except wearing and displaying clothes hires two con-men weavers who promise him the finest, best suit of clothes from a fabric invisible to anyone who is either unfit for his position or "hopelessly stupid".
Split into simpler sentences: A vain emperor who cares about nothing except wearing and displaying clothes hires weavers who promise him they will make him the best suit of clothes. The weavers are con-men who convince the emperor they are using a fine fabric invisible to anyone who is either unfit for his position or "hopelessly stupid".