Verbal wishes will not be binding under California law. A will, or a "codicil" to a will would have been necessary. If you try to remove your brother based on duress or undue influence, that will not help to enforce "verbal wishes."
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It is true that verbal wishes are not legally binding on the executor if property not specificed in will. However, if all family members unite and agree that the verbal wishes should be honored and each receive what they were promised, the executor has a moral duty to comply. Family pressure is the only way to go.
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I agree with both counsel here. The decedent's verbal wishes are not a substitute for a will. Hopefully, she also expressed those wishes to the brother, that he will agree to follow them and the rest of the family (those named in the will) will go along with it.
The information you obtain at this site is not, nor is it intended to be, legal advice. You should consult an attorney for individual advice regarding your own situation.