Legal Question in Family Law in California

Unless your husband had a will leaving property to her, your sister in law has no rights to his property. If he had no will, everything he owned is yours now, though you may need to open a probate if he had anything of value that was not community property. Also, if you have children, some of his property probably legally belongs to them. But without a will specifically leaving property to them, brothers and sisters have no right at all to a deceased person's property, unless the person dies with no living spouse, no living children, and no living parents.