My sister is marrying a guy with whom she has lived for six years. They are inviting his ex-wife and many of her relatives to the wedding. One of his ex's nieces will even be in the wedding party. I feel it is tacky to have his ex-wife at the wedding, although they have a grown daughter together and have stayed good friends. It just doesn't seem appropriate. Am I wrong?
You are completely entitled to your opinion, and it's true that in most cases such an arrangement wouldn't be possible. But as long as your sister is okay with it, it's completely fine. If she's not okay with it, that's a different story -- it's her wedding, and she has a right to feel comfortable! If she's upset about it, encourage her to confront her husband-to-be with her feelings. He needs to know about them -- before they head down the aisle.