Try this one on
:
We have person A and person B. They get married. Person A is the youngest in his family. He has an older sister (we'll call her C). C has a son, D. Person B is the oldest in her family. She has a younger sister, E. D and E meet, fall in love, and get married.
It doesn't stop there. A and B have a son (F). C's husband (G) , has a brother (H) who has a daughter (I). Later on, F marries I.
There is no inbreeding here at all (except for A and C's paternal grandparents, who were first cousins) - but it makes for interesting relationships. For example: A is D's brother-in-law and uncle. The children of A and B are D's neices and nephews and cousins. The children of A and B are related to the children of D and E through both sides of the family (they are first cousins, and first cousins once removed). The children of D and E are related to the children of F and I three ways (They are first cousins once removed and second cousins twice).
The children of D and E are related (by blood) to everybody that the children of A and B are related (by blood) to (although the reverse is not true). The children of F and I are related (by blood) to everybody that the children of D and E are related (by blood) to (although, again, the reverse is not true).