Some of the imagery used to describe the husband (Stanley) reveals much about his character. When the family awakens after their first night in the house, Stanley is doing exercises in front of his wife and is described as "glowing" and "squatting like a frog" as he does his exercises. His body (which he quite admires) is described as "firm" and "obedient." This imagery strongly suggests that Stanley is somewhat vain, but he reveals very soon thereafter that he is also more than a little insecure. He worries that he will one day become fat, like some men of his age already are.
As for the aloe plant, the imagery used to describe it emphasizes that it is strange and unusual to Keziah, underscoring (like the wallpaper decorated with parrots) the strange new surroundings the family has moved into. The plant is described as "fat" and "swelling" and as having "cruel leaves." The encounter with the aloe plant, which is contrasted with the other familiar plants elsewhere in the garden, is at the center of the narrative—indeed, "Prelude" was initially intended to be part of a novel entitled Aloe.
As for the dog, his name is Snooker. In the words of one literary critic, he is described as "endur[ing] treatment that oscillates between care and cruelty." The dog is ugly, and it smells bad. The boys are always concocting some bizarre chemical mixture to give him for reasons that are not exactly clear. He is himself somewhat wild and has to be restrained when the boys kill a duck at the pond. Like the aloe, the dog is on the edge of wildness and civilization.