Hi. I have no experience obtaining records from Napa State Hospital, but was able to obtain an ancestor's records from the facility that holds, the now defunct, DeWitt State Hospital patient records.
We had to provide proof of kinship, which included birth certificates that showed the line of descent, complete a records request form, and provide a photo ID. Once we submitted the completed forms we received the documents fairly quickly. However, the file we received was not complete (six pages for a 20+ year incarceration) and were told by the record holder that the files were probably not properly maintained over time.
Good luck, and feel free to message me if you have any questions.