Hades- Brother of Poseidon
Hades is the ruler of the underworld, and is married to Persephone. His symbol of power is the cap of invisibility.
Zeus- Brother of Poseidon
Zeus is the brother of Poseidon, and the almighty ruler of the gods. His symbol of power is the Lightning Bolt, and his relationships with women are always changing.
Demeter- Sister of Poseidon
Demeter is the sister of Poseidon and the goddess of the harvest. She rules over the grains and the fertility of Earth.
Hera- Sister of Poseidon
Hera is the sister of Poseidon and the goddess of women and marriage. Hera is known the be the jealous type, and would punish all of the lovers of Zeus.
Hestia- Sister of Poseidon
Hestia is the sister of Poseidon and is the virgin goddess of the hearth and architecture.
Amphitrite- Wife of Poseidon
Amphitrite is the wife of Poseidon, and the Goddess of the Sea.
Cronus- Father of Poseidon
Cronus if the father of Poseidon, and is married to Rhea. He is the leader and youngest of the first generation of titans, and was overthrown by his own son Zeus. His symbol of power is the sickle or scythe.
Rhea- Mother of Poseidon
Rhea is the titaness daughter of the sky god Uranus, and wife of Cronus.