N-648 medical certification for disability exception question

[GDT47 0]

Hello All,

 

any advice on my dad situation;

He is 78 years of age and just had an interview last week, submitted the form N-648 accepted and approved by the officer. Before the interview officer mentioned that the N-648 got approved but my Dad still needs to do the reading part and writing. My dad can able to read but barely. Unfortunately when the officer told him to write, he can't write the word clearly. I was surprise that he can't write, probably because of his medical condition, he had a history of stroke years ago. He don't understand English at all, he used to understand and at-least can communicate but now is just zero understanding on English language. (The doctor only check the part for the civic question and not the speak and writing in English.) The officer then told him to wait for another interview notice to challenge just the writing part. 
I posted, this already on Reddit and one told me to post here.
-reddit people told me to have my dad doctor corrected the N-648 and check the civic part, writing and speaking in English. 

-on part 4. Ability to understand Oath of Allegiance, should the doctor answer yes or no. ( I can explain Oath of allegiance to my dad)