The "A Family's Legacy" side quest is automatically unlocked after the "United Front" main mission in Sequence 7. To complete the Sphinx riddle and get the "Riddle Me This" achievement, complete the "A Family's Legacy" (Thera), "Lore Of The Sphinx" (Boeotia Region), and "Awaken The Myth" (Boeotia Region) side quests. Simply complete the side quests to fight him.
The Minotaur is the endboss of this questline, found in the Labyrinth Of Lost Souls.
To fight the Minotaur boss and get the "A-maze-ing Victory!" achievement for defeating him, complete the "Myths And Minotaurs" (Messara Island), "Of Minotaurs And Men" (Messara Island), and "He Waits" (Messara Island) side quests. Medusa is a Level 50 boss - so you need to be at least Level 46 to have a chance. All of these quests take place on Lesbos Island, which is a high-level endgame region. Medusa is the endboss of this questline, found in the Petrified Temple on Lesbos. To fight the Medusa boss and get the "In Perseus's Image" achievement for defeating her, complete the "Romancing The Stone Garden" (Lesbos Island), "Love's Long Shadow", "Hard To Artemis", "Heavy Is The Spear", "Keys To Happiness?", and "Writhing Dead" side quests. The Cyclops of this questline is a high-level one-eyed monster. Note: This has nothing to do with the Sequence 1 story boss that has the same name. As part of this questline, you will find the Cyclops boss on the Forgotten Isle (he is not accessible outside of this quest). To fight the Cyclops boss and get the "Eye On The Prize" achievement for defeating him, complete the "A God Among Men" (Kythera Island), "Left To Dye" (Kythera Island), and "Stairway To Olympos" (Kythera Island) side quests. Name of the file: Assassin's Creed Odyssey - Xbox One - Author: ANO.