YOU SAID:
Today is the birthday of aunt Astrid
INTO JAPANESE
今日はアストリッドの叔母の誕生日
BACK INTO ENGLISH
Today is the birthday of my aunt Astrid
INTO JAPANESE
今日は叔母のアストリッドの誕生日
BACK INTO ENGLISH
Today is the birthday of my aunt Astrid
That didn't even make that much sense in English.