Dialysis is not started based on a single number or test. Dialysis is started when the patient and his nephrologist think that there could be a benefit of dialysis and the risks are understood and agreed to. The questions that you ask are very good and need to be asked of the nephrologist and physician who are treating him. I am unable to make any specific diagnosis based not the information that you present. I also cannot recommend treatments without performing a complete history and physical examination. I would be concerned about the possibility of dementia, delerium or other causes of your step-father’s reluctance to follow medical advice and non-adherence to his medical treatments.
I suggest that you write these question down and ask his physician and his nephrologist to discuss this with you and your mother. Your step-father may also need further examination and consultation.