well, there are many ways to look at this, and it goes down to motives. You have a relationship with your in-laws. You may have met them because of AH, and blood is thicker than water, but that does not deny the reality of a relationship you have pursued and built with them, I don't think that wanting to talk to them is necessarily about their relationship with him, very few marriages exist in isolation from their wider families. Many spouses seperating for whatever reason DO explain their motives to their in-laws, because these are people that they are fond of and have built relationships with. I imagine their are a wide range of experiences regarding the outcome, and time may help you decide whether in your circumstance it is worth doing.
I haven't discussed my motivation with my in-laws, they are aware of the problem, although not the extent or the behaviour that went alongside it. They ask, and I am uncomfortable discussing it because any answer I give, (completely truthful from the hip, sugar-coated, evasive) ends up with some sort of drama which I can't be bothered with.
You may have a different relationship with your in-laws, I am very fond of mine and want to continue to support our children having a relationship with them, but I won't discuss x as it never turns out well.