The Smiths are visiting us this Christmas.
Mr and Mrs Smith have four daughters, each of whom have a husband, two brothers and two sons.
How many people should we expect, so we can work out the size of our turkey?
Actually only four.
Each of the Smiths daughters will have taken her husband's surname, and thus her sons will have that surname too. So the four Smiths are Mr and Mrs Smith and their two sons, who are the brothers of their daughters.
Yes, we do know that nowadays woman don't necessarily take their husband's surname, and that the husbands could be called Smith; however this is a Christmas puzzle, so please don't shout.