can we write our own will? how does the state recognize it is legally binding?

There are 3 ways to write a valid will in CA. A holographic will is one on a blank page, completely in your own handwriting, signed and dated.  No notary or witness is required.  Second, CA has a statutory will online which is simply a form to fill in which requires 2 adult disinterested witnesses.  Third, an attorney can prepare a more formal will which also requires the signature of 2 adult disinterested witnesses.  Remember, though, that a will DOES NOT  avoid probate.