You can probably get some information by requesting certificates from the Civil Registries. Visit:http://www.mjusticia.gob.es/cs/Satellite/en/1200666550200/Tramite_C/1214483951490/Detalle.html
There you can find English-language pages that will let you request those certificates. Civil registration in Spain started in 1871. Barring accidents, floods, war, etc., you should be able to find those certificates.
From 1840 to 1871, a first attempt at civil record keeping was attempted. Implementation was irregular and conservation of these records is uncertain. If existing, they are kept at the municipal archives. Access to those archives is not uniform, in some towns may be easy, in others may be impossible.
Before 1871, your best chances lie with the Catholic Church records. Since roughly everyone was a catholic, their christening near birth, their marriage(s) and burial were recorded in the parishes and they provide important information, including in many cases name and origin of parents and grandparents. Depending on the year and on the parish, records might be at the Historical Diocesan Archive o at the parish itself.
But first, try to extract all you can from the civil registries.