Allsorts
If you think it's acceptable behaviour, I don't, but it takes all sorts. Should the son leave his wife because she ignores his mother and father or extend any courtesy? Totally unrealistic, he's his children to consider for a start off. Ma and Pa have to accept she's rude and just say hello and goodbye with a smile on their faces. Children grow up, marriages end. Who knows what the future holds.
I think people should say hello and goodbye whilst smiling. However, I'm not agreeing to the notion OP was treated as a leper - which was my point.
If I were to speak to anyone (and I doubt I would) I'd speak to my own son as I'd have raised him and have a relationship going back years.
I'm not sure why OP speaking to son is totally unrealistic, he's his children to consider for a start off. Of course he has children, I wasn't advocating to speaking in front of children or leaving his wife.
However his parents went to his on Christmas, presumably invited by him -- perhaps that's enough?