Everybody at Collinwood is being very silly. It's very annoying, but very believable.
Sarah tells David, "Don't go near the Old House." David knows she's a ghost. He knows she has special information. So what does he do? He goes to the Old House. And then Roger and Elizabeth just pooh-pooh what David says, instead of sitting down with him and getting him to tell the whole story, from beginning to end, of why he believes Barnabas is bad. Of course it wouldn't do any good because David feels bound by his promise to Sarah to keep the secret of the room in the mausoleum - but Roger and Elizabeth still should make the effort.
This is the episode in which Julia says that Willie has been delivered to a home for the criminally insane. If he had gone to Windcliff, she would have said so.
I agree with lori54: that scene with the bat terrorizing David was a good one. But I don't agree with lori54 about Jason McGuire: bad as he was, he hadn't earned the death penalty.