looking for some perspective with fiance's family
I'm not quite sure what to make of this situation and could use some perspective.
History: My fiance and his ex have been divorced for 4 years after 15 years of so-called marriage. She cheated on him constantly and is now married to the last guy she was cheating with. Those 2 had been "together" for 5 years before the divorce. She finally left my fiance when she inherited a large sum of money (she was never one to actually work, you see, so she'd stayed with my fiance for his money, which wasn't a lot but was comfortable enough) and moved herself and their 2 kids (son, 12, and daughter, 17) across the country. They worked out an agreement re:custody just fine, except that she says the kids don't want to see him and she can't make them. He hasn't seen his kids in a year and a half and hasn't even spoken to his son in 8 months ("I can't make him answer the phone!" is her excuse). His daughter calls him when she wants money, and ONLY then. His family is horrid to me. 2 years ago, his daughter told his family that I had called her a slut. Without asking if it was true, they all started throwing me attitude at the family reunion. I finally confronted one of them, who spilled that little fact. It was kind of a shock, considering I don't even use that word. Lately the daughter has been even more bold in her lies and accusations, and I'm sick of it. BM has refused for years to get this girl some treatment, and now that she's almost a legal adult, I'm afraid it may be too late. But I digress. Anyway, my fiance tried and tried to communicate with his ex for the kids' sake, but she wouldn't answer her phone and would send him emails which didn't relate to whatever he'd been asking about. About 6 months ago, she just stopped communicating altogether (it had been sporadic at best anyway). Fiance's family is totally aware of what's gone on and how he feels about everything.
Fast-forward to Thanksgiving. His sisters got together and invited the ex and kids and her husband (yes, the one she'd cheated on fiance with for 5 years) to Thanksgiving at one of the sister's houses. They didn't invite their brother. In fact, they hid it from him. He found out about it that day! Mind you, we went to Thanksgiving at my ex-mother-in-law's house, but my XH and his wife came, too! But I talk to my ex. We all get along because we know it's important for the kids. (My family doesn't talk to my ex, but they have no reason to.)
Anyway, fiance was pretty upset. I was, too. He's an awesome guy and doesn't deserve to be treated with such utter disregard.
Any opinions? Comments? Helpful hints? I've cut them out totally (fiance says I'm really good at burning bridges, but I didn't see a bridge there anyway), but that's his family.
tl;dr version: fiance's sis invited ex to t-giving, not her own brother. help?