Here are two explanations about who the guardians are and what the shadow realms might be in these two works:
The Guardians in the Hero's Journey pattern are figures who inhabit the unknown world that the Hero enters. They are protectors of this special, unknown world and will in some way challenge or test the hero, trying to prevent his or her entry into the new world. They "are not the main villains" that the hero will encounter on his quest, but they are "lieutenants of the villain." Christopher Vogler, author of The Writer's Journey: Mythic Structure, says, "Think of the doorman at Oz and the wicked witch's monkeys. The guardians are "naysayers, doorkeepers, bouncers, bodyguards, gunslingers," and I am quoting this from the site About.com, which gives a pretty good summary of the Joseph Campbell ideas that go back to psychologist Carl Jung's foundational work on archetypes.
The Shadow Realm is a place like the Wicked Witch's castle in the Oz stories or the Lonely Mountain where Smaug resides in J. R. R. Tolkien's The Hobbit. It is a dark place that the hero must enter into and destroy or redeem. In modern works, this place of darkness might be a dark psychological state that must be encountered in order to face frightening and repressed parts of the hero's own nature. Think about Holden Caulfield's fears and recent traumas in Catcher in the Rye.
So think about how these phases of the motif/archetype apply to Telemachus' and/or Odysseus' journeys into the unknown and back to Ithaca, which has become a dark place! It's not the same place that Odysseus left when he sailed off to Troy almost twenty years earlier. Think about how these phases might apply to your hero or heroine in the modern odyssey. Again, don't worry about being "right"; just let these ideas be ways to see why the author includes these phases in a hero's journey. What do these phases tell us about our own quests and "journeys," the literal ones and the psychological ones? We will be discussing these ideas in class! But come with some ideas, some speculations about why this archetypal pattern taps so deeply in the consciousness of human beings. See you soon!