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Sthenno and Euryale.
Stheno and Euryale, Medusa's sisters, were immortal and could not die.
of the three Gorgon sisters, Stheno was the eldest, Euryale the middle, and Medusa the youngest.
No: Oenopion is a male mortal.
Euryale the Gorgon was the daughter of goddesses either Gorgo or Ceto.
Poseidon and Euryale