Legal Question in Wills and Trusts in California

Unless you have evidence to present in a court of law that proves it is more likely than not that there was a will, you can't do anything if your dad is lying. All community property goes to the surviving spouse to do with what they like. However, without a will, if your mom had any assets that were her separate property your dad is entitled to keep 1/3 of the separate property, you should have gotten 1/3 and your sister or her kids should have gotten the other 1/3.