If you are a family member of a European Union citizen and you are going to reside in Spain for a period of more than three months, then you must apply for a supporting document:
Be an employee in Spain.
Be self-employed in Spain.
Have sufficient financial resources for themselves and their family members so as not to become a burden on the social assistance system of Spain during their period of residence.
In addition, you must be related to the Union citizen as follows:
If you are a family member of a student, you may be:
Spouse, Partner with proof of cohabitation, Son or daughter of the Union citizen or of his or her spouse or registered partner, any member of the family who in the country of origin is dependent on or lives with the Union citizen, any member of the family whose situation, for serious reasons of health or disability, makes it strictly necessary for the Union citizen to take care of his or her personal care.
In other cases it may be:
Spouse, partner registered in a public register established in an EU Member State or in a State party to the EEA, direct son or daughter, direct ascendant, any member of the family who in the country of origin is dependent on the citizen of the Union, among others.