Hummmm, clearly you and Denver are not parents of M kids nor have grandchildren....
Well, I have been in that uncomfortable seat from both sides and I still say to respect what his parent's want in their home. As I told one of my kids once, I wasn't the one that fell in love with your S, so you need to give me more time. Any parent will feel by their grown children just like they did when they were little and somebody hurt them.
If you push this on the parents, not only will they feel that's unfair (and it is), but the WAW will be able to feel the tension and that her in-laws are having to strain to be nice. That is certainly not going to help matters, in fact, she'll use that as an excuse...not the other way around.
The WAW needs to suffer loss! Come on, you guys! She needs to experience the consequences of her decisions. How is that enforcing any questions about her decisions? She needs to be concerned about what friends and family think.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!
