There will be 4 golems to kill in the Eternity vault, each one will become invulnerable when it is close to dead. Have someone click on the scroll stand associated with that type of golem to break the enchantment and kill it. Once all four are dead the Guardian of Eternity will automatically attack. Kill him and the blue and purple gems will lower down and can be moved.
Place the blue gem on the pedestal in the Keeper of Dream's room. Place the purple gem on the pedestal in the Keeper of Nightmare's room. Now the final door for Praetor of the Phylactery will be unlocked.