Demeter is a Goddess, an Olympian, a daughter of Kronos and Rhea. She is by no means a demigod.
She had an affair with the demigod Percy
Zeus, Poseidon, Hades, Hestia, Hera, and Demeter.
Yes: Persephone.
No, Hestia did not have any demigod children, she was a virgin goddess.
No, she was not. Demeter had children.
No she does not.
Yes, Demeter did have children, such as Persephone (goddess of springtime).
No. Since Artemis is a virgin goddess, she can't have any demigod children.
No, Hades has no children.
Demeter had one daughter with Zeus: Persephone.
Other names for Demeter include Ceres (in Roman mythology) and the Great Mother.