[Edited by Latiosmaster47, 5/1/2010 5:58:19 PM]
I hope this won't be the case, but in all likelihood their kid will have down's syndrome or severe genetically-based diseases that will kill him/her young, or leave him a vegetable or mentally stunted for life. This is part of the reason why Incest is illegal.
I don't think Incest should be illegal per se, just discouraged. Consent between adults is consent between adults. I'm actually quite fond of the whole "Twincest is Wincest" thing within the fandom, and a LOT of good stories and artwork depict twins discovering their feelings for each other.
But I digress, the age-factor is the most disturbing thing about this. The rest is not so much disturbing as it is unsettling. Pearl will probably pass away before the kid's 10th birthday (Average life expectancy of a white female is around 86-88 or so years, but she doesn't look to have aged gracefully to put it lightly).
I'm pretty sure incest should be illegal. "Discouraging" something won't stop it, especially without any punishment. No one wants the amount of mentally challenged people to increase, that's why some governments try to keep them from breeding. If incest were made legal, all those efforts might very well be neutralized.
Give the lucky couple their prize because it seems they succeeded.
I feel bad for that kid. Could you imagine finding out your mom is also your great grandmother and your dad is one sick ****? This kid will either run away or become a serial killer.