YOU SAID:
I'm a disappointment to my family
INTO JAPANESE
私は私の家族に失望しています
BACK INTO ENGLISH
I am disappointed with my family
INTO JAPANESE
家族にがっかりしました
BACK INTO ENGLISH
I was disappointed in my family
INTO JAPANESE
家族にがっかりしました
BACK INTO ENGLISH
I was disappointed in my family
That didn't even make that much sense in English.