Four people are sitting around a campfire after a long day of recreation, when one man comments: "Do you realize that around this campfire, the four of us include a mother, father, brother, sister, son, daughter, niece, nephew, aunt, uncle and a couple of cousins"?.
If everyone is related by blood (with no unusual marriages) how is this possible?
He doesn't say anything to indicate that, for instance, any of the four is the uncle of any of the four, simply that there is an uncle present. It is the same for each of the roles named.
Actually the man could have said the same thing if only he and a woman were there: He could be a father, brother, son, nephew, uncle and cousin; she could be a mother, sister, daughter, niece, aunt and cousin.