We all are going to age one day and God help the family member who does not care for their own mother. Thanks for your story. Caregiving is about families, the strengths and weaknesses. Your grand is lucky she has you. When you personally do all you can, you are the one who can sleep at peace at night.
Some family members are afraid.
Using the talents of other family members can also be helpful. One may not be able to be there physically but maybe can do something to contribute from afar. Forgiveness is also a powerful tool for all to practice. His situation is stable and they will take care of him for the rest of their lives. I have another friend who cared for her husband who had a severe stroke.