Rather than fighting this battle yourselves, see if you can enlist a professional social worker. If your father has been hospitalized recently, call the hospital's social work office. If he has been on dialysis (you mentioned renal cell CA), there should definitely be a social worker in the picture. They do this stuff (like battle Social Security) all the time and may know some tricks. Your dad is to be praised for his valiant efforts but he is likely to get more and more tired. Rally the troops to come to his aid.