I've only heard of one family where there were two cases. This is such a complicated syndrome!
Though the causes for Scimitar syndrome are ideopathic. It appears it is not genetic, but if it prevails in the family the chances of a child born with the defect seem to be a factor. With that information, it is difficult to rule out a genetic predisposition! Any comment?
Have you considered writing this on the Rare Disease Forum?