Background & Context:
My wife has two brothers, Bob and John. With Bob and his wife there is absolutely no problem. We help each other out when there is something to do and get along really well.
John and his wife, however is a different story. They are both narcissistic, egoistic, and enjoy making fun of and patronizing everybody else in the family (me, my wife, Bob and his wife and even the parents). John´s behavior seems to be getting worse, it is not improving.
It has been suggested that we sit down and discuss these differences. I have already told my wife that I don´t want to participate in this meeting for several reasons, none of which add any value to this situation.
It's safe to assume that I will never get along with John and his wife. The extent of my interactions with them involve saying hello and goodbye in passing, this is all I wish to maintain.
Expectations of me:
My wife has told me that during the sit down she will ask for my opinion if I don´t say anything myself, because she considers it important that I tell them how I see their behaviour and that I´m not happy with their personalities, as well as the way they treat people around them.
The Interpersonal Problems:
Firstly what persuasive or linguistic approaches can I take to convey that I do not want to attend the meeting or at the very least do not wish to contribute.
Secondly if I have to attend, in what way should I frame my distaste for John and his Wife's actions and personality that would come across as constructive rather than personal or aggressive, as I would at the very least prefer not to make the situation any worse than it is.