Legal Question in Wills and Trusts in California

If she had a valid judgment against him at the time of his death, she can make a claim against the estate if there is still time. If she recorded the judgment with the county recorder, there is a lien on the estate, you will get a phone call from the executor followed by a check. Watch out for short legal time limits.

Your brother and you may have a claim if there was no Will as you are his children.

Your mother doesn't have any claim, based on the scanty information that you have provided.

If your mother has a court order for child support, she can make a creditor's claim against your father's estate. Based on your post, I am presuming that your mother's "ex" was not your father. In that case and if your brother's father died without a will, your brother may be entitled to an intestate (without will) share of your father's estate under California Probate law. The proportion share of the estate to which your brother may be entitled to depends on whether the decendent had other children or whether he had other children at the time of his death.