Why do the family members try to avoid talking of the ghost?

Initially, the family avoid talking about the ghost because of the blood-stain in the library (in Chapter Two). Washington Otis removed it with Paragon Detergent but its continual reappearance troubles the family:

The whole family were now quite interested; Mr. Otis began to suspect that he had been too dogmatic in his denial of the existence of ghosts, Mrs. Otis expressed her intention of joining the Psychical Society.

After this incident, the family spends the day driving and talking of all manner of subjects which detracts their attention from the Canterville ghost. Arguably, they do this for two reasons: firstly, because they are afraid that the ghost really does exist and that more supernatural events will happen. Secondly, they avoid talking about him because they do not want to accept that they were wrong about the existence of ghosts. If they did this, it would be tantamount to admitting that their scientific and rational view of the world was wrong. This is fact that the Otis family are not quick to accept, considering Mr Otis's defence of science and the "laws of Nature" in Chapter One when he debated the existence of the ghost with Lord Canterville.