My FI has three nieces ages 15-18 who are spoiled rotten by their parents and grandparents. (MIL gives money as their mom is always crying poor, however the new hardwood floors and marble tub didn't install themselves, but I digress) and I know these girls will want to bring a friend to the wedding even though they'll most likely be texting/FB'ing the whole time. (none have steady boyfriends). His sister will allow it and just not tell us before hand, they'll simply show up with three extra people in tow yet the gift amount will not cover extra plates. I know I will lose my cool. Any ideas how to quash this before it starts?
Tidbit: Grandma bought the oldest TWO $600 prom dresses as she was going to 2 dances at different schools. Those cost more than my wedding gown!