Is the wife's father entitled to intervene in the marital home's affairs by asking about the monthly expenses and the husband's treatment of his daughter in his absence, and is it permissible for the wife to reveal her home's secrets to her father and brothers, and what is her punishment if she does so?

The affection of a father and a grandfather is strong and does not end with the marriage of a daughter or granddaughter. A father has the right to inquire about his daughter's well-being to reassure himself, just as Ibrahim (peace be upon him) did when he asked his son Isma'il's wife about their situation. However, a father should not inquire about details of their living expenses, such as the amounts the husband pays, as this is not good manners and may spoil the relationship with the son-in-law.

A grandfather also has the right to check on his granddaughter in a wise manner that does not cause problems or create suspicion.

As for a wife divulging her husband's secrets, this is impermissible because it is a betrayal of trust, and revealing someone else's secret is worse than revealing one's own. However, the husband should not harbor ill suspicions about his wife as long as she has denied revealing the secret, and her words should be taken as truthful unless her falsehood is proven.