The Greek Gods were one big happy, or not so happy, family. When reading their mythology it can sometimes be confusing to try and remember exactly how they are all related. Here is an overview.

In the beginning there was Chaos. From Chaos were born five beings: Tartarus, Gaia (Earth), Eros, Nyx (Night), and Erebus. Two unions came from these five: Gaia with Tartarus, and Nyx with Erebus. From the union between Nyx and Erebus came Aether and Hemera. Erebus fathered many other children, although I'm not sure with whom. They are Momus (blame), Ponos (woe), Moros (fate), Thanatos (death), Hypnos (sleep), The Hesperides, The Keres and Fates, Nemesis, Apate (deception), Philotes (friendship), Geras (age), and Eris (strife). From the union between Tartarus and Gaia came Typhon. Gaia also had other children, again I'm not sure with whom. They were Uranus, The Mountains, and Pontus.

For some reason Gaia mated with her son Uranus. From that union came the Titans and monsters. The monsters were Echidna, Hecatonchires, and the Cyclopes. The Titans were Mnemosyne, Chronus, Rhea, Coeus, Phoebe, Iapetus, Oceanus, and Tethys. Hyperion was also born from this union although he was neither monster nor titan.

Oceanus mated with his sister Tethys and they bore the Oceanids: Melia (who was a daughter of Oceanus but not of Tethys), Inachus, and 3000 other sons and daughters. Melia and Inachus are named because they got together and bore Io. Pleione was also a daughter of Oceanus and Tethys but is not named among the Oceanids.

From Iapetus came Epimetheus, Prometheus, and Atlas. Atlas mated with Pleione and from them came the Pleiades: Maia, Dryope or Merope or Aero, Asterope, Canaeno, Electra, Alcyone and Taygete.

There were two other unions between the Titans. Coeus and Phoebe bore Leto. Then there's Chronus and Rhea. From them came Hestia, Hades, Hera, Poseidon, Demeter and Zeus.

Zeus got around, a lot. He was married to Hera, but he slept with Demeter, Mnemosyne, Semele, Alcmene, Leto, Dione, Maia, and Io. And those are just the recorded ones. Due to all these unions he had lots of children. From Semele came Dionysus. From Alcmene came Herecles. From Mnemosyne came the Muses: Calliope, Clio, Erato, Euterpe, Melpomene, Polyhymnia, Terpsichore, Thalia, and Urania. From Hera came Ares, Hebe, and Hephaestus. From Demeter came Persephone. From Leto came Apollo and Artemis. From Dione came Aphrodite. From Maia came Hermes. From Io came Epaphus. Zeus also fathered Athena who supposedly came out of his head fully grown.

Hermes united with Aphrodite and they had Tyche, Rhodos, Peitho, Eunomia, and Hermaphroditus. Hermes also mated with Dryope and they had Pan. Hermes also fathered Abderus.

The gods of Olympus were Zeus, Hera, Poseidon, Demeter, Hades (although he spent most of his time in the underworld), Dionysus, Hebe (she gave up her position after she married Heracles), Hephaestus, Aphrodite, Apollo, Artemis, and Hermes.

Most of these names have stories attached to them. Greek mythology is fraught with incest, adultary, rape, murder, intrigue, patricide, murder, war and all sorts of other nasty things. Most of these stories and family ties can be found in various places on the internet.