Miss Manners: I received a ‘save the date’ for a party where I only know one couple

Dear Miss Manners: I received a “save the date” email from a friend’s sister. She described how the family was going to celebrate all the milestones occurring this year, including my friend and his wife’s 50th wedding anniversary and the milestone birthdays of 13 other family members. They have rented a very prestigious venue that will easily hold several hundred people. It has been billed as a no-gifts event.