Legal Question in Wills and Trusts in California

"Declaring" a person dead is not a concept that has any legal meaning. What matters under the law, no matter where a person dies, is who can sign a death certificate. In most states, and I believe in CA, only an MD or licensed Nurse Practitioner can sign a death certificate.

People die at home all of the time, thankfully, given that most would rather die at home instead of in a hospital. Usually an autopsy isn't required as long as the decedent's physician signs off as to the cause of death. Death Certificates are usually available within a week or two unless there's an investigation.

That is usually a matter for the coroner.