The fact that you and your sister are married and that your brother was adopted are irrelevant, of course your names have changed and an adopted child has the same rights, in this respect, as a birth child. If your mother made a valid will some 16 years ago which did not include your brother as a beneficiary his only claim will probably be under the Financial Provision of deceased’s estate, nothing to do with his or your name, hopefully the will is stored in your solicitor’s strong room.