It depends on whether your brother had a will. If he did, then the named beneficiaries under the will have that right. If he did not, then the property passes by the law of intestacy.
I assume that your brother was not married or did not have a registered domestic partner. Under this assumption, based on what else you have stated about your brother, and assuming that California's intestacy law applies, the property belongs to your mother.
You probably should meet with a probate lawyer who can review all the facts and give you a better opinion than what you can get in a public forum like this.