Your mother could have had a so-called "no contest clause" in her will, which means that if anyone who is a beneficiary of the will contests the validity of it (or any of its provisions), that beneficiary will be precluded from getting his/her share under the will.  That said, a no-contest clause (in California) is strictly construed to determine the intent of the testator (your mother), as well as the no-contest clause can only be enforced in certain instances, depending on the reason for contesting the will (California Probate Code Section 21311).  You should read carefully all of the provisions of the will to determine whether the no-contest clause of your mother's will is enforceable in your situation.