Can an illiterate spouse be a patient representative for social security?

My father has Alzhemiers and has applied for SSI. He is 63yo currently on Cobra for his health care insurance. My Mother is unable to read or write in any language and refuses to accept the fact my father is ill. She was allowed to sign as his representative at the SS office. She does not drive, can not write or deposit checks and refuses to let me the daughter take over as the representative. My father knows he is ill and that he can not take care of her and himself as he did in the past. He has a Dx from his Neurologist and is currently receiving SDI. I am afraid my mother will throw away important papers, forms or information sent in the mail. Who is suppose to pay the morgage, groceries, utilities ect.. I am stuck! My mother is being very stubborn and refuses to accept my father's illness. She has always been very dependant on my father for everything. She has also been emotionally unstable my entire life ie.. OCD, fears being alone, strange rituals.. but she has never seen a provider so she is not Dx as mentally incompatent. She is making my father drive her to church everyday, even though his license was revoked. He got into an accident last week and she said " Oh it could have happened to anyone" I am at such a loss..please help!!!