DEAR MISS MANNERS: We’re at a bit of a loss regarding beach house invitation etiquette. We purchased an eight-bedroom second home with the idea of hosting family, friends and acquaintances throughout the season. We provide 5 p.m. cocktails and casual dinners for anyone wishing to join. Our idea has been “the more, the merrier” — many of these people have met previously and get along, plus we truly enjoy seeing everyone together. Most guests seem to enjoy themselves immensely and write lovely notes in our guestbook. But to our surprise, several people have been unhappy to learn they will not b…