This is very sad indeed. I think with advent of sperm banks, these kinds of accidents are going to become more common.
As much as I sympathize with the couple, I hope that they annul the marriage and seek other partners. I am critical of first-cousin marriages too still practices in some societies so for me this is clear case of incest, even though unknowingly. Good that there is no child involved like the German couple we discussed about few months back where a brother and sister had couple of children and most with genetic disability and low IQ. The probability of recessive genes is high as proven in many Royal families.
Laws and society are made by humans to bring a certain discipline to life. If everybody objects to law's interference and wants to lead their life as they prefer then there would be anarchy and probably new laws need to be formed thenđ.