My wife's sister is causing me and my wife a lot of stress. Her sister is the older of the two siblings and has always been one of her parent's favorites, so they let her get away with everything. She is 25 years old and I am marrying her younger and only sister who is 23. I myself am 27 and am older that her sister and her sisters husband. Since my wife's sister married her husband she has turned even worse. He sister's husband is well off and makes a high salary so immediately her sister started to treat other people as if they are beneath her. She routinely disrespects my wife and myself; an example (her husband and her would come to her parents house and would not greet me as part of the family, not a hug, not a hi, how are you, not even a kiss my ***. She would just completely ignore me)
When there is a family gathering everything has to be about her. The conversation has to be about what she is doing at work or something that she likes, and if the topic changes to something she isn't interested in or if the attention is off her she immediately starts to sigh, make little comments and just generally acting like a spoiled brat. My wife has talked to her family and has expressed how she feels her sister is treating me and nothing has been done. They treat her sister as if she cannot do anything wrong.
We are supposed to have a family gathering tomorrow and I am dreading it. I do not want to even be around her sister at all. I love my wife's parents and love being around them, but when I hear that her sister is going to be there I immediately get filled with dread. I've tried everything to just ignore her remarks, but that is not making things better. I've expressed to my wife my feeling and she has talked to her parents but I do not know what to do? I would like to be around her whole family but her sister is making it really hard to deal with.
Anybody have any advice? Like I've said before I've ignored the slights, I've expressed my feeling to my wife, and I've even kind of spoke up to my sister-in-law as well and nothing has gotten better.

