Yes, their daughter was Persephone.
Zeus
There was only one child between Zeus and Demeter, and that was Persephone.
Zeus loved Demeter and had Persephone.
Yes, with both Demeter who he had Persephone with, and with Hera who he married.
Persephone, daughter of Demeter and Zeus, became Queen of the Underworld with Hades as King.
Demeter is Zeus' older sister
Zeus is the brother of Demeter
Demeter had one daughter with Zeus: Persephone.
Persephone's parents are Zeus and Demeter.
Zeus and Demeter were not lovers. Demeter bore a daughter by Zeus named Persephone (Kore), however Zeus married his other sister, Hera. (Note that Zeus mated with many other goddesses and mortals, not just his lover and Demeter)
Hestia, Demeter, Hera, Hades, Poseidon, and Zeus were the children of Cronus and Rhea.
No. Demeter is the daughter of Kronos and Rhea. She and Zeus are siblings.