nina first let me say I am sorry your sister is sick.
if it were me I would bring my sister home with me. how long are they giving her at this point? maybe make a temporary truse with your dad until she is gone. I know it would be very difficult to do and with hospice help you could manage that I think. if your dad would agree to set up his visits with her so hospice could come sit with her even so you would not have to be there. just an idea but I do hope something works for you and your family.