rights as a patient advocate

My grandmother has been found incompetent by a psychiatrist and physician. She cannot care for herself, and my grandfather has cancer and cannot care for her either. She has lived with me in the past because he couldnt take care of her. I am an RN student and I currently work as a medical assistant in a cardiology office. I am also a CNA. I am my grandmothers Patient advocate, and I need to know if i can legally keep family and my grandfather from putting her in a nursing home? Please help.