Kristin Scott Thomas did not play William's wife. as a matter of fact, she wasn't even in the film. this film is definitely one of my all time favorite movies. i don't know how many times i have seen it, but i still find new things. Samantha Morton always delivers. this movie is something to pay attention to because we are heading down this road. however, genetic testing could be done to make certain that even if they were related, they did not carry the genes that would cause defects. there is a Jewish tribe that has a lineage of inbreeding and except for TA Sachs's the children are of superior health and intelligence. the only time incest of this nature (where neither person actually knew each other prior to the 'coupling) is an issue is where introducing one set of genes from one parent would not cause problems but if both have the defect then yes, it would be advisable to not let the intimacy occur.