YOU SAID:
my brother and sister died last week
INTO JAPANESE
私の兄と妹は、最後の週に死亡
BACK INTO ENGLISH
My brother and my sister died last week
INTO JAPANESE
私の兄弟と私の妹は、最後の週に死亡
BACK INTO ENGLISH
My brother and my sister died last week
That didn't even make that much sense in English.