My in-law's wife routinely screams at and insults his mother and brother (but not nec. him) - he is humiliated. is that spousal abuse?

Bigger problems: The term "abuse" doesn't really clarify anything or facilitate understanding of the problem. It probably depends how you define the word "abuse." the important issue is that there is a serious problem in the relationship. It's time for the couple to begin a meaningful conversation about what is going on between them and how it is affecting their relationship. Therapy may be in order.

Perception: Whether some behavior is considered abusive is dependent on whether that person is being abused. If he is humiliated and feels as though he and others are being abused, then yes. If he does not feel that he the spouse is being abused then no.