The California Health and Safety Code lists the persons who have the right to make decisions about disposition arrangements after an individual's death unless other written instructions are left.  They are listed in the following order:

Decedent

Agent under a Power of Attorney for Healthcare

Spouse OR Registered Domestic Partner

Child / Children (majority)

Parent / Parents

Sibling / Siblings (majority)

Grandparents, Granchildren

Great-Grandchildren, Nephews, Nieces, Uncles, Aunts, Great Grandparents

All persons must be competent.  And, Except for spouses and parents, all persons must be at least 18 years of age.  Domestic partners must be registered with the Secretary of California.

Decedent's wishes must comply with the Health and Safety Code Section 7100.1 to be binding.