I REALLY need advice ex and family issue

My husbands ex wife of only 4 years and NO children together, continuously has contact with his family. They ignore me/us and see her often to the point of 'helping her out' when she needs it. Both my husband and myself are livid that they have turned on him/us for her. We just don't get it. She is a sociopath and they cannot seem to see it. She had multiple affairs and left him. WTH? They send Christmas cards to her and also to my husband exclusively, but not to me or my children. Its so hurtful. Here is where I need the most help right now. His sister has a picture posted on her FB page of their family with the ex wife sitting on my husbands lap. What do I do with that? Course hubby doesn't want to rock the boat but I feel extremely disrespected. I had a friend of mine ask me if we were still married b/c they saw that picture. Am I making more of this? Should I just let it go? I dont think I can. I am so bothered by it. Please help. :(

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