They are referred to be so common place that they are barely noticeable at all, and properly speaking only the sister served briefly providing narration on the Jack of Fables books. The whole family is only showed briefly having a picnic.
The Walls are the personifications of the metaphorical walls inside which the performance is undertaken. The first three walls refer to background, stage left and stage right. The fourth wall being the one that separate the audience from the performers.