Wow, that's a shame. It sounds like your family's already being very accomodating of your wife...that's asking a lot, not to mention a birthday because it might offend her. Couldn't she meet them halfway, and attend, then? Why not tell her, you'll respect her feelings if she wishes to stay home, if she respects your desire to attend your sister's special event!In other words, let her sit home by herself, but don't let her spoil it for you! After all, when will your sister get engaged on her birthday again, can't miss that!
Sorry, should have clarified. I am indeed going but I have kids who are barred from going. Turning up and having to explaining all this crap does my head in.