Hera, Hestia, Demeter, Zeus, Poseidon and Hades are all brothers and sisters.
Hera is married to Zeus, who cheats on her with just about everyone he can. Hera always goes after the 'other woman' with a vengeance, even when it's rape. They have one child: Ares, who is a disappointment (too emotional). Hera also had Hephaestus (no father), but she didn't like him either (born with a club foot).
Artemis and Apollo are Zeus' twin children by Leto (an affair). Athena is Zeus' child by Metis, his first wife. Zeus heard that Metis' son would overthrow him so he swallowed her when she was pregnant. Some time later Athena was born full-grown out of Zeus' head, in armour with spear (think business suit with briefcase), with no memory of her mother and total loyalty to her father. Hermes is the son of Zeus and Maia. Dionysus is the son of Zeus and Semele (who died before giving birth, so Zeus sewed Dionysus up into his thigh and gestated him himself). Aphrodite is the daughter of Zeus and Dione in one version, but in the other she is born out of the sea foam after Uranus' (Zeus' grandfather) genitals are cut off and thrown into the sea (and therefore is older than Zeus). Either way she's a law unto herself.
Artemis, Athena and Hestia never marry, although Artemis had a boyfriend (Orion the hunter) at one point. She killed him in a competetition by mistake. Demeter has a daughter, Persephone, by Zeus (one of his earlier marriages, before Hera, who is wife number seven).
Persephone is abducted by Hades with Zeus's permission, but in the end decides to marry him and spend part of the year in the underworld with him, and the rest above ground with her mother.
Aphrodite is married to Hephaestus, but carries on a long term affair with Ares. She and Ares have three children: Phobos (Fear), Deimos (Terror), and Harmonia (Harmony, sometimes known as Discord, her other aspect). Aphrodite and Hermes have a bisexual child called Hermaphroditus. Eros (Cupid) may be her son, with no father. Aphrodite also has an affair with Adonis, a variation of Dionysus, who is slain by a boar sent by the jealous Ares and ends up spending four months of the year with her, four months with Persephone in the Underworld, and four months recovering from both of them.
Poseidon is married to Amphitrite, but cheats on her, and then has to win her back (oops!). Apollo is single. Hermes is single, but is paired with Hestia in temples (she inside, he outside the door). Dionysus is initially single, but then marries Ariadne, a variation of Aphrodite, and they party on. Dionysus, incidently, is the dying god (like Adonis) and therefore is also seen as the consort/son of Persephone, queen of the Underworld, and the above ground aspect of her husband Hades. Hades tried to get it on with a couple of other women but it didn't work, since he just isn't smooth enough (unlike Zeus and Poseidon), so it looks like he's a one-woman man by default. (Though it's interesting that Freud (Poseidon) and Adler (Zeus) were not philanderers while Jung (Hades) was.)
Famous Couples (+ some successful marriages in my family)
Artemis and Zeus
Lucille Ball and Desi Arnaz (1940 - 1960, ended in divorce)
Artemis and Poseidon
Mary Shelley and Percy Bysshe Shelley (1814, m. 1816 - 1822, ended in his death)
Artemis and Hermes
Amelia Earhart and George Palmer Putnam (1931 - 1937, ended with her death)
Artemis and Dionysus
F. Scott and Zelda Fitzgerald (1920 - 1940; ended with his death)
Athena and Zeus
Hilary and Bill Clinton (1975 - )
Athena and Apollo
Margaret and Denis Thatcher (1951 - )
Athena and Hermes (in mythology: Athena and Odysseus)
Simone de Beauvoir and Jean-Paul Sartre (1929 - 1980; ended with his death)
Hestia and Poseidon
Gene Roddenberry and Majel Barrett Roddenberry (1969 - 1991, ended with his death)
Hestia and Hermes
Hume Cronyn and Jessica Tandy (1942 - 1994, ended with her death)
Hestia and Apollo
George W. and Laura Bush (1977 - )
Hestia and Hephaestus
Alfred Hitchcock and Alma Reville (1926 - 1980, ended with his death)
Hera and Zeus
Norma Shearer and Irving Thalberg (1927 - 1936; ended with his death)
Hera and Poseidon
Laurence Olivier and Vivien Leigh (1940 - 1960, ended in divorce)
Hera and Hades
Humphrey Bogart and Lauren Bacall (1945 - 1957, ended with his death)
Hera and Apollo
Jacqueline and John F. Kennedy (1953 - 1963; ended with his death)
Demeter and Apollo
George and Barbara Bush (1945 - )
Persephone and Hades
Charlie Chaplin and Oona O'Neill Chaplin (1943 - 1977, ended with his death)
Persephone and Dionysus
Elizabeth Barrett Browning and Robert Browning (1846 - 1861, ended with her death)
Aphrodite and Ares
Goldie Hawn and Kurt Russell (1983 - )