What is the ruling on sprinkling water and salt on the thresholds and corners of the house to expel devils, and what should be done to fortify the house and repel harm from it, especially when there is suspicion of it being afflicted by envy?

The use of salt to ward off devils has no basis in the Book, the Sunnah (definition), or the practice of the Salaf. Some contemporary scholars have permitted it, while others have prohibited it, and it is preferable to abandon it. As for reading the Qur'an into water and sprinkling it in the corners of the house, that has been answered previously. Purifying the house from pictures, statues, and dogs is correct, because they prevent the entry of angels. Reciting Surat Al-Baqarah is one of the greatest means of expelling devils from the house.