Tree:

Well, what a letter indeed. Sorry you found it and had to endure the emotional blow of reading it. Yes, we can rationalize how we might expect this from in-laws but reading it still hurts. Anyone reading such things about themselves would be hurt.

I concur that you must not respond. Let go of the things you cannot control. I don't see any good whatsoever for you in responding--no good at all on any level. Vent here, or to others in your personal life. You won't change anyone's mind by responding, and might do/say something that could bite you in the D. Even something that sounds benign might get interpreted later in ways you never meant. So don't even go down the road. Keep your head up, keep finding joy for yourself when/where you can, keep feeling the pain when it hurts, and keep believing that you are a good and worthy person who has and will continue to have a good life no matter what happens to you. Do not resist the situation as it is; learn from it and stay away from W and any of her family. They are not your friends right now, and may never be again.