YOU SAID:

my brother has a mother my mother is my brothers mother

INTO JAPANESE

私の弟には母親がいます 私の母は私の兄弟の母親です

BACK INTO ENGLISH

my brother has a mother my mother is my brother's mother

INTO JAPANESE

私の弟には母親がいます 私の母は私の弟の母親です

BACK INTO ENGLISH

my younger brother has a mother my mother is my younger brother's mother

INTO JAPANESE

私の弟には母親がいます 私の母は私の弟の母親です

BACK INTO ENGLISH

my younger brother has a mother my mother is my younger brother's mother