You know, I never thought a lot about the OM and his family's role in the situation. My situation is a bit unusual so I won't go into detail here, but my wife is in an EA, and she knows his very well. I feel like his family has played an active role in our divorce because they've always supported her and believed everything she said.
My sons are old enough that they can have a say in what they're exposed to; they don't like the OM or his family. They think the OM is creepy.
Along the way, there were many times when I felt like the OM's family was more important to my wife than her own family. Yuck!