It must be the Lawyer gene.
Seriously, your cavalier and judgmental comment, or should I say decree, seeks to punish all for the sins of the two lesbian couples.
Somehow, these two children of deviates managed to develop normally as heterosexuals and until the hidden facts came out, were leading a normal and respectable life. This isn't like an Oedipus story, for heaven's sake! Let them live out their lives as normal folks!
That’s just the point, bud. The truth will out. Now that dad knows he is married to his sis, the vibes will start. The kids will sense it, even if they haven’t been told. What, you suggest he continue to have intercourse with his sister? Good grief, man, who is the brute in this situation?