I think his home life is extremely important. He does get contradictory messages from his parents, but also, he doesn't seem to be getting very much moral guidance either. There's not much in the way of teaching virtuous Christian behaviour, which I find odd, considering his mother's devoutness. She condones his lying, his stealing, the killing the chicken, in effect. She passes no comment about the chicken, expresses not even surprise, even though it hasn't been killed in the correct manner. It needed challenging. This is the child who tortures animals. (BTW, what are we to make of the fact that he crucifies a rat?) She lets him know that she knows he's been stealing money, but that isn't good enough. It's plain wrong to steal, and she should have had that discussion with him. I wonder if he hadn't been told that in no uncertain terms, whether he would have taken the cameo. And how does she deal with him pushing his brother through the window? Arturo is surprised that she has snitched on him to his father, and she defends him in front of Svevo with 'boys will be boys'. I don't mean to suggest that I am excusing Arturo's behaviour. He does some monstrous, hateful things, but he thinks he can balance them out with confession and being an altar boy. He doesn't take responsibility for his own actions, or appreciate the worth of good deeds. August seems to be making the same mistake, too. In the end, I think it comes down to accepting responsibility for actions and problems, something which none of the family seem to be able to do. Arturo runs to church to offload his sins and then repeat them, and when the priest gives him some practical advice how to make it right, he won't do it; Svevo blames everyone else for his troubles but himself; Maria just prays to solve her problems. I'm not knocking the praying, just that she doesn't do do anything else to solve them. Even she acknwowledges that she is asking a bit much in praying for her husband and her mother to get on, but doesn't change.
In the end, this creates a lot more problems for herself. I think this theme of individual responsibility is key, and it is touched on very early in the book, with August's bedwetting. They all have had this debate about why he has stopped. Personally, I go with August having willed it.
"Luck... inspiration... both only really happen to you when you empty your heart of ambition, purpose, and plan; when you give yourself, completely, to the golden, fate-filled moment."