Your dad is married to your mother, not you. It's his responsibility to see she's cared for; that's what the marriage vows mean when they have you promise. . . "in sickness and in health" and "Therefore a man shall leave his father and mother and be joined to his wife" (Genesis 2:24).

When my mother died my father and grandmother tried to make my aunt give up her life and come take care of me and my three brothers. My grandfather put a stop to that.

I recommend doing what is right for you.