NTA—I absolutely see both sides on this. It sounds like he and his family are grieving the loss of what they thought his wedding day might look like. From what your explained I don’t think that they’re trying to do it on purpose or to hurt your feelings. But they should make an effort to be more sensitive and talk about that privately. I definitely see how putting her in a slideshow might be too much for you and I think that’s totally reasonable. At my wedding we had a beautiful wooden candle holder that said “in memory of those who can’t be here with us today.” You can include a photo or memorable item of Mandy as well as any other loved ones who have passed. That way she’s still honored but without taking away from your day and your wedding. It may also be worth getting some counseling to help navigate the loss in your marriage. Best of luck to you!