CA Fam Code Section 9303

(a)

A person may not adopt more than one unrelated adult under this part within one year of the person’s adoption of an unrelated adult, unless the proposed adoptee is the biological sibling of a person previously adopted pursuant to this part or unless the proposed adoptee is disabled or physically handicapped.

(b)

A person may not adopt an unrelated adult under this part within one year of an adoption of another person under this part by the prospective adoptive parent’s spouse, unless the proposed adoptee is a biological sibling of a person previously adopted pursuant to this part.