They do and that is why they were concerned as they know the history.
That is exactly what I figured there was a history between you and the mother in law, no better time to turn up the heat than when the wife is away all stressed out on a new project.
but that doesn't give you the right to be the moral crusader of family life.
I am no moral crusader, but I have seen it all here in PL, I have also been in the company of many Brits here that constantly want to change all things Polish to all things British.
I am happy for you that you have found a good relationship with yours
It did not come easy we both had to grow up to the situation.