Legal Question in Family Law in California

Yes, it's called incest. "Marriages between parents and children, ancestors and

descendants of every degree, and between brothers and sisters of the half as well as the whole blood, and between uncles and nieces or aunts and nephews, are incestuous, and void from the beginning, whether the relationship is legitimate or illegitimate." (Fam. Code, sect. 2200.)

It would also be a crime. "Persons being within the degrees of consanguinity within which

marriages are declared by law to be incestuous and void, who intermarry with each other, or who being 14 years of age or older, commit fornication or adultery with each other, are punishable by imprisonment in the state prison." (Penal Code, sect. 285.)