Lanzo, Not sure if there was a question or a request for advice in that last post. The family thing can be difficult. I know I said too much to some of my family about what was going on in our S. I was looking for advice and support, but in hindsight you end up with difficult situations like this.
Since you are posting in this forum, I take it that your W is on the same page as you (or almost) that you both want to fix the M. Part of this will also include repairing relations with the in-laws. Maybe this is just too soon, but I would encourage your W to attend the party. It seems like it would be a non-confrontational situation where your family could see that your W is with you, committed to the marriage and willing to make amends with your family.