What are Persephone's and Hades' similarities?

Zeus is the brother of Hades.

Zeus is the brother of Demeter.

Demeter is the sister of both Hades and Zeus.

Persephone is the daughter of Zeus and Demeter: making her uncle Hades.

Persephone is a goddess of Spring who became Queen of the Underworld.

Hades is a god of the unseen who became King of the Underworld and the riches of the earth.

They are then both earth gods/goddesses, and related to each other as well as being the rulers of the Underworld.