Hello Camille

You need to contact the Spanish embassy and ask them to give you the list of documents for your father to start a Spanish Nationality recovery application via their Civil Registry section. Once your father has the Spanish Nationality, you can apply by Option as Spanish by origins.

You can read about the particular procedure by clicking here:

http://www.mjusticia.gob.es/cs/Satel...os-adquisicion

The option to apply based on the LEY DE MEMORIA HISTORICA is no longer valid, as there was a limited period of time to apply that ended in December 2011.

Regards,