As befitting a gothic tale, Poe uses many parallels to construct this masterful story of horror and dread. However, two of the most striking that, to me, are central to the story and its impact are the parallel between the House of Usher and its inhabitants, and the parallel between Roderick and his twin-sister, Madeline.
When we are first presented with the House of Usher, the description immediately establishes a link between the setting and the people within it. The House is described as follows:
Its principal feature seemed to be that of an excessive antiquity. The discolouration of ages had been great... In this there was much that reminded me of the specious totality of old woodwork which has rotted for long years in some neglected vault, with no disturbance form the breath of the external air.
Images of rotting and disintegration abound, just as in the description of the house's owner, Roderick Usher, who is described as being half-dead, with a "ghastly pallor of the skin, and the now miraculous lustre of the eye." Both house and owner are in a dilapidated, half-dead, rotting state.
Note too how another parallel is established between Roderick and Madeline concerning their description. For Madeline, too, is described in terms that present her as half-dead/half-alive, which ironically leads to the confusion (or deliberate mistake) of her entombment whilst still alive.
The joint death of these twins therefore, seems to be fitting, as does the destruction of the House of Usher at the end of the tale as the narrator flees the site of such terror. It appears that a bond united the ancestors of the House of Usher with the House itself so that they shared a similar fate - in life and in death.