If my mother died after my brother died does his children have any rights to my my moms estate she left no will we live in the state of 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.