Information on Demeter's family tree can be found on GreekMythology.com and Wikipedia. Demeter is a Greek goddess whose parents were Cronus and Rhea. Her brothers include Hades, who abducted Demeter's own daughter Persephone; Zeus, the king of the gods; his wife Hera and Poseidon.
Zeus, Demeter's brother, was also the father of Persephone. She also had sons by Iasion, another child of Zeus. These sons were Ploutos, Philomelus and Korybas.
The most popular story concerning Demeter was her grief at losing her daughter to Hades. As she searched the world for her, plants ceased to grow and began to die. Eventually, it was agreed that Persephone could return to the world for what became the growing season and return to her husband for the four months of winter.