What is the religious ruling on dealing with the husband's father who interferes excessively in the couple's life and abuses them, knowing that he does not pray and threatens divorce? And how can ties of kinship be maintained in this difficult situation?

The father-in-law has no authority over his son's wife, and the husband is not obligated to obey his father in divorcing his wife, especially if the father is tyrannical or ill-mannered. It is advisable not to rush into seeking divorce, but rather to try to reform the husband and demand a separate home to avoid escalating problems with the father-in-law.