What is the ruling on a widow and her daughters living in her husband's father's house?

There is no harm for a widowed woman and her daughters to live in her husband's father's house with his consent. The husband's father is a mahram (definition) to his son's wife, as stated in the verse: "And not display their adornment except to their husbands, or their fathers, or their husbands' fathers, or their sons, or their husbands' sons" (An-Nur:31). It must be noted that a woman whose husband has died must observe her iddah (definition) in the house where her husband died and she was in it, and she should not move to another place unless there is a necessity.