Ah, I can see it that way too now.
The answer I was looking for was 'fourth cousins'. Elrond was a fourth cousin to his own children as follows:
1st cousins: Luthien and Earwen
2nd cousins: Dior and Galadriel
3rd cousins: Elwing and Celebrian
4th cousins: Elrond and Elladan/Elrohir/Arwen
Following the line as you did shows that Elrond and his grandson were also four
![Stick Out Tongue](http://forum.barrowdowns.com/ubb/tongue.gif)
th cousins!
Do you suppose that all the inbreeding is what caused their ears to be pointed?
Since your answer is correct, it is your turn!