California Probate Code section 8221 provides that a will can be proved by proof of the testator's handwriting and proof of the handwriting of one of the witnesses. If you cannot prove the handwriting of one of the witnesses, you can submit an affidavit of a person with personal knowledge of the circumstances of the execution.
You may need to do a little detective work to find the witnesses or the attorney who drafted the will. If you know the name of the lawyer who drafted the will, check the State Bar website to see if s/he is still practicing. The witnesses are probably people who worked for the lawyer at the time (paralegal, another lawyer in the office, etc.).
You might also try the local county bar association. If one of the witnesses was a paralegal or legal secretary, chances are other estate planning lawyers in town know her/him or know people who are friends of his/hers.
It sounds like you're trying to do this on your own. If you continue to run into difficulties, you should consider hiring a probate lawyer to assist you.
The information you obtain at this site is not, nor is it intended to be, legal advice. You should consult an attorney for individual advice regarding your own situation.
I would only add that Section 8221 of the Probate Code does provide that if the will "on its face conforms to all requirements of law" the court may permit proof of the will by proof of your father's handwriting and (b) a document "reciting facts showing execution of the will" by (i) "a writing in the will bearing the signatures of all subscribing witnesses."
To take advantage of this provision you definitely need to consult with a probate attorney.
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