Is the electricity bill considered a debt upon the deceased, or must her daughter and her husband pay it?

If the agreement between the sister, her daughter, and her husband was for everyone to bear the electricity bill, and then the sister promised to pay it in full from her own money (including the share of her daughter and her husband) and she passed away before paying it, then this is not considered a debt upon her. The daughter and her husband must bear their share because it was a promise of a gift that was not fulfilled.

However, if the sister provided housing to her daughter and her husband as a charitable act, and explicitly stated that she would bear the entire electricity bill without burdening them with anything, then the value of the bill is a debt upon the deceased sister, and the daughter and her husband are not obliged to pay it except as a voluntary act.