My mother passed with no will ... I was living with her and now one of my sisters wants the house to go to her son who doesn’t even live in the area.C

When someone dies without a Will, their estate can be settled via an Affidavit of Small Estate or an Application for Determination of Heirship, depending on the amount in the estate and on other questions.  You may well need to settle your mother's estate by hiring an attorney to help you file an Application for Determination of Heirship.  After paying the debts, it will be distributed to her children (assuming her spouse left his 50% community property share to her), not to a grandchild who is the child of a living child. Until the court appoints someone to settle the estate, no one has authority  to live in the house or to evict someone else who is living there.