A will generally needs more than one witness in every U.S. state that I have ever heard of. The witnesses need not be notaries, however; neither is being a notary a bar to being a witness to a will.
The attached California statutory information, relating to California Probate Code sections 6110-6113 may be helpful. I cannot vouch for its currency, however. Statutes are often read in conjunction with case law in which judges interpret the meaning of various terms. I make no representation as to any applicable case law.
Consult a California lawyer if you need legal advice. This is not legal advice as I do not hold California licensure or practice law there.
You need at least two disinterested witnesses. The mechanics of executing a Will must be strictly followed. A Will can be witnessed by a notary but an acknowledgement is not necessary and an acknowledgement would not substitute for either or both of the required two subscribing witnesses.
I am licensed in California only and my answers on Avvo assume California law. Answers provided by me are for general information only. They are not legal advice. Answers must not be relied upon. Legal advice must be based on the interplay between specific exact facts and the law. This forum does not allow for the discussion of that interplay. My answer to any specific question would likely be different if that interplay were explored during an attorney-client relationship. I provide legal advice during the course of an attorney-client relationship only. The exchange of information through this forum does not establish such a relationship. That relationship is established only by personal and direct consultation with me followed by the execution of a written attorney-client agreement signed by each of us. The communications on this website are not privileged or confidential and I assume no duty to anyone by my participation on Avvo or because I have answered or commented on a question. All legal proceedings involve deadlines and time limiting statutes. So that legal rights are not lost for failure to timely take appropriate action and because I do not provide legal advice in answer to any question, if you are an interested party you should promptly and personally consult with an attorney for legal advice. Also, see Avvo's terms and conditions of use, specifically item 9, incorporated by this reference