I think they just fell out of love with each other, maybe after sometime apart they will get back together (though I suspect they have already had time apart before announcing their split) but otherwise maybe they will follow the example of Anne and her ex who lived close by to each other and even worked together on evening activities at Gatcombe. Also at the moment neither probably has a new partner so of course this is going to keep going, once/if they get new partners they may not be quite as willing to appear together. Anne is very practical IMO and if as we read she is already made clear she is happy to provide housing at Gatcombe, I think she knows whatever else Autumn is still the mother of her grand-daughters so she is going to keep things civil for them if nothing else.
No every one who gets divorced has to hate their ex so I think they are doing just fine, I don't think this was forced or fake.
I completely agree. Anne's branch has always been the reasonable and practical one. Plus Peter and Autumn are adults that can be trusted.
They surely won't break up a fight, not only for the sake of their children, but mostly because they're not the type for drama.