21. Zeus not only married one of his sisters, he also had a child with another one. Who was she?
From Quiz The Messy Family Life of a King of the Gods
Answer:
Demeter
Demeter, goddess of the harvest and agriculture, was the second child born to the Titans Cronus and Rhea: her siblings, besides Zeus and Hera, were Hestia, Hades, and Poseidon. All of them were swallowed by their father, who feared being overthrown by his children, but eventually rescued by Zeus, the youngest child, who had been saved from the same fate by his mother. In Hesiod's account, Demeter was the fourth of Zeus' wives, with whom the king of the gods fathered Persephone, goddess of seasons, originally named Kore ("The Maiden").
When Hades, god of the underworld, fell in love with Persephone, Zeus helped him to abduct her, as he knew that Demeter would never allow Persephone to go to live in Hades' underground realm. Demeter, devastated by the loss of her daughter, vowed not to allow anything on earth to grow until Persephone was returned to her. Zeus then ordered Hades to return Persephone to her mother - which he did, though not before having tricked her into eating a few pomegranate seeds before her departure. Because she had eaten the food of the underworld, Persephone would be forced to spend part of the year with Hades, ushering the arrival of winter.
Dione, who was either a Titaness or an Oceanid nymph, was one of Zeus's divine consorts, and - according to some accounts (such as Homer's "Iliad") - Aphrodite's mother.