In Harper Lee's To Kill a Mockingbird, Bob Ewell is a drunken, lazy, abusive man. He does not work, and his oldest daughter takes care of the younger children. He is essentially "white trash," considered by his neighbors to be at the bottom of the social ladder, but he himself considers himself better than any black man. (This is ironic in that Tom Robinson, the man he falsely accuses of raping his daughter, is a much finer man that Bob Ewell could ever hope to be.)
Mayella is the product of her environment. She is crass; she seems to be high strung (understandable when looking at her father). She is left to take on the role of the mother, caring for all of her younger siblings, and their home. Her life is lonely and ugly. People comment on how unusual it is to see geraniums growing on their property: their home is a hard place to live, planted in the midst of squalor (poverty) and filth.
Mayella's relationship with her dad is not a good one. Bob is physically and verbally abusive. From Tom we hear that Bob Ewell calls her a whore when he sees her with Tom Robinson. It is proven in court that she has been beaten by her father. She is petrified of him, and would never think of saying anything in court that her father did not want her to say.
There is a puzzling comment that Tom makes when Mayella tryies to get him to kiss her.
She reached up an' kissed me 'side of th' face. She says she never kissed a grown man before...She says what her papa do to her don't count.
Nowhere in this novel does Bob Ewell come across as an affectionate or caring father. Mayella says that what her father "do to her" does not count. This makes me wonder if Ewell is also sexual abusive toward Mayella.
There is no question that Bob Ewell is a man without a conscience; he has no concern for lying, beating his own daughter, or sending an innocent man to his death (probably the sentence Tom would have received had he not tried to escape). Mayella has learned to do what she is told, and the reader witnesses first hand what happens to her when she crosses Ewell. (We see his abusive nature again later when he goes after Atticus' kids.)