The Question and Answer section for The Fall of the House of Usher is a great resource to ask questions, find answers, and discuss the novel.
I can give you a few: foreboding, depressing, morose, apprehensive, dark, bleak, deterioration.....
I believe that Roderick helps the narrator place Madeline in the coffin. She was not in the coffin when the story started.
The entire family tree is pretty thin: there is a direct line of descendants, meaning in-breeding has taken place.