I think you must be the male version of me (say what?). I would have and did react to things pretty much the sameway until some really smart people pointed out that for so many reasons I may want to rethink how I react.
I love what Lissie, Ian & SmartCookie had to say and I'm not sure I can add anything more worthwhile to what they addressed, but something else did jump out at me and it was in regard to FIL. You aren't really sure why FIL would do what he did, but do you think that possibly he reacted to something SHE may have told her Dad? I say this because my inlaws were really up in arms about what ex was doing, until he gave them some lame ass excuses as to why. He told them some awful off the wall things. As they say "blood IS thicker than water" and in the end, they want to believe that there is more of a reason than to have to face that their kids is just plain screwed up.