That is why you shouldn't marry cousins. Centuries of inbreadin has festered into severe psychological problems.
Seriously though this problem/problems won't be solved until these people stop listening to radical religious leaders tell them what the Quaran says (or any of the numerous supporting texts) and figure it out for themselves. Kind of like how the West stopped listening to the calls for "Crusade" and for the most part "Kill the Jews" by corrupt power hungry religious leaders. They still don't understand why we made seperation of church and state a law. Precisely because power corrupts and absolute power(i.e. I speak in God's name) corrupts absolutely.