I think all the tribes are what we would call incestous (except for the Gliders perhaps, for they stopped breeding within the first 1000 or so years). To a degree that it would be impossible for us humans to survive more than three generations under the same conditions... I guess.
Elves seem to be less prone to the undesirable effects of inbreeding. Thus its no tabu. And its tabu/immoral for us only because the offspring of closely related parents... well... you know, will likely be not too tightly wrapped in their heads. Plus some other disadvantages.
In the history of humankind incest hasnt always been banned. And when I look at our european royal houses, that can be very obvious. Rumours have it that its no coincidence many of the young royals here chosing their partners from us "peasants" instead from other houses. You know, fresh blood and all....
ANYWAY... elves dont have this problem so our moral codex doesnt apply.
Also, I like Icetooth' idea of a recognition between Timmain and Aurek very much.
Better go now.