In the state of California, can a 16 year old ask for a custody hearing to disolve parental guardianship and then have guardianship granted to someone who is not related?

No, a 16 year old could hire an attorney and seek emansipation, but the people he wants to become legal guardian, will have to bring the court action and prove your current parents are unfit, and that they are a danger or they are some threat to the 16 year old.