Spanish Law 1770 in Mexico

Spanish Law or Custom 1770
What was the Spanish law or custom about 1770 in Durango, Durango surrounding this event? Pablo Lucio Padilla married Maria Gertrudis Godoy. He was a free mulato, she a mulata slave belonging to someone else. Did Pablo have to buy her? Did she remain the slave of the 3rd party? In giving consent for the marriage would her freedom also have been included without comment in the church record? Would their children be free?, or slaves of the 3rd party owner?
Thanks. Ed Nissen Padilla