II had a friend who married a Muslim. For 12 years they kept the secret from her parents. They thought that Andy (my friend) was just a housemate. According to her sister, they apparently believed it. Then they wanted a family, so the secret went. Her family haven't spoken to her since.

Of course, it could have gone the other way with Andy's family. Point is, the family believed (hoped) they were housemates, even though in reality only an idiot would think that.