Is a son sinful for not loving his abusive parents, and how can he repel their injustice against his wife while still honoring them in a way that pleases Allah?

Feeling hatred towards one's parents is not a sin, as long as one does not actively cause it or outwardly express it. It must be suppressed and not shown to them. They can be advised and admonished with wisdom and good counsel, without argumentation or raising one's voice. Furthermore, the wife can be moved to a separate dwelling to avoid conflict, and she should avoid anything that provokes them and strive to be dutiful to them.