How can the questioner's parents' house, which she feels is impure and fears the transfer of impurity from it to her own house, be cleansed?

Leave aside doubts and whisperings [from Satan]. What you are not certain is impure, is, by default, pure. What you are certain is impure, can be purified by pouring water over it. If you are unable to do that, the impurity of those places does not harm you, because dry impurity does not transfer to dry pure objects it comes into contact with. You may also adopt the view of the Hanafis, who hold that impurity does not transfer to pure objects that are wet or moist, in order to remove hardship and difficulty.