Evidence includes testimony of witnesses and documents that support your case. Witnesses are people (including you) and documents are papers. At least 5 calendar days before the hearing, you and the regional center must exchange lists of witnesses and copies of the documents you want to use in the hearing.§ 4712(d). That means both you and the regional center should have each other’s documents and witness list 5 days before the hearing. The witness list must shortly describe what each witness will testify about. The judge may not let you present witnesses and documents if you do not tell the regional center about them 5 days before the hearing.
To have a witness who will not agree to testify, you must subpoena them. A subpoena is a legal order forcing them to attend the fair hearing to testify. Subpoena witnesses and ask them to testify as soon as you get a hearing date so people will be available. Hearing forms, including the subpoena form are here: https://www.dgs.ca.gov/OAH/Case-Types/General-Jurisdiction/Forms/Page-Content/DDS-Forms