They are the three daughters of Phorcys and Ceto.
Phorcys Phorcys
There is debate on who is Scylla's parents, the list is the following (father and mother): Typhon and Echidna Triton and Lamia Phorcys and Hecate Phorcys and Crataeis Phorcys and Lamia Phorcys and Ceto Poseidon and Crataeis
Phorcys the Shieldless was killed by Ajax, King of Salamis.
Phorcys and Ceto
Yes, he was.
Medusa was the child of Phorcys and Ceto, who in turn were the children of Gaia and Oceanus.
Yes, they were Ceto and Phorcys.
Phorcys and Ceto.
Gaia (Earth) and Pontos (Sea).
Phorkys and Ceto
No, Phorcys and Ceto were godly.