They did clear the date with the SIL. She said it was fine but then changed her mind after they got officially engaged. I guess I just don’t understand how marking one day on your calendar two months before your wedding could possibly be SO stressful. At least call it what it is- you wouldn’t want a sibling upstaging your wedding by doing it first. In the grand scheme of things this is all falls down to two days in their lives. I get being annoyed. But if this is really gonna determine the relationship with your in-laws for life, I guess you got bigger problems than choosing a wedding date.