Complex sentence: Hubert comes back to the Desouche house, looking like a Zombie because he has different body parts from many different corpses, and when he sees Mother sleeping it becomes apparent that it is not Hubert at all but Angus dwelling in the mangled body.
Split into simpler sentences: Hubert comes back to the Desouche house, looking like a Zombie made of different body parts from different corpses. When he sees Mother sleeping it becomes apparent that it is not Hubert at all but Angus dwelling in the mangled body.