Legal Question in Wills and Trusts in California

Yes, if she lived in California when she died. Since she did not have a will or a trust, then her estate passes by intestate succession which means that your brother's children would share his portion of the estate.

For this answer, I am presuming that you and your deceased brother are your mother's only children and that her spouse predeceaed her. In that case, you would be entitled to 1/2 of your mother's estate, while your brother's surviving children would each be entitled to equal shares from his 1/2 of the estate.