Can a friend's parents enroll me into high school?

I’m 17 and will turn 18 in about 10 months but my parents want to send me back to the US to finish senior year there. Since I’m a minor, will a notarized and signed temporary custody letter be enough for her parents to enroll me into a school in California? I emailed the school but haven’t gotten word back from them yet and I need to know soon if this is possible. Thank you!

This is a question that might be answered by an attorney.