Frankly I can't understand why everybody seems to be equating a relationship between Skywise and Timmain as incestuous.
I think I heard after 7 generations, people are no longer considered to be genetically related, even if they have a common ancestry. For example: Take a pair of siblings. They meet their respective loves of their lives and have children. Repeat this 5 times, and 7 generations have passed. By then so much different genetic material has been introduced into the family, that even if a pair of those 7th generation descendants meet and have children, it is not considered a case of inbreeding.
Admittedly Timmain is still genetically the same as when she founded the Wolfriders. But since then 10 generations of chiefs, and probably more generations of tribesfolk have passed. There's even been genetic mutations, the elves got smaller. It's not exactly as if it's next of kin we're talking here!