See now here's where we're getting into sources.
My sources disagree with yours, that's all.
Mythology by Edith Hamilton, one of the most noted writers on Classical Mythology, lists the Olympians as being Zeus, Hera, Poseidon, Hades, Athena, Apollo, Artemis, Aphrodite, Hermes, Ares, Hephaestus, and Hestia.
Zeus's brothers being Poseidon and Hades, and his sisters being Hestia and Hera (also his wife). His children were Ares, Athena, Apollo, Hermes, and Artemis. Sometimes also considered his children were Hephaestus and Aphrodite.
These are the 12 great Olympians. The gods of Olympus, who reside therein.
Demeter and Dionysus were considered Earthly Gods, because they did not reside in Olympus, and instead delighted in the revelry of man, who worshiped both as great gods of the earth. Demeter for providing the Harvest, and Dionysus for providing the wine.
While other lesser gods did live in Olympus (not to be mistaken with Mount Olympus, a different place), they were not considered to be part of the Great Olympians, for their role was lesser in regards to man's life. These gods were Eros, The Graces, The Muses, Hebe, and many others, though less often mentioned. There were also ideals who had become embodied that resided in Olympus. These were Themis, Divine Justice; Dike, Human Justice; Nemesis, Righteous Anger; and Aidos, the sense of respect and shame that keeps humans from sinning.
