Why don't the Franks just lie about being Jews and not worry about the dictatorship of Adolf Hitler and go on living their lives?in The Diary of Anne Frank
It would not have been easy for the Franks to lie about being Jews. They had been living in Amsterdam for many years, and they had attended religious services and gatherings during that time. Their neighbors, schoolmates, and business associates would have known that they were Jewish. Some of those people most likely would have turned them in just to save their own lives or gain favor from the Nazis. In fact, some historians believe that it was a neighbor who disliked Mr. Frank who did turn them in when they were hiding in the attic. No one knows who made the anonymous phone call to inform the Nazis about the family. See the articles in the sources section for more info.
I agree that they probably realized someone would turn them in, and that even though they may have considered this, it would have been distasteful to them since they were proud of being Jewish.
In addition, most families of Jewish descent did not realize just how much trouble they were in for being Jewish until it was much too late to do anything about it. No one wanted to believe the horror stories, and most simply chose not to listen until the horror story was on their own doorstep.
The Nazis had such complete control over any area they conquered that they were able to get full lists of all the Jews in any city. The Franks could not have claimed to be Gentiles without fear of someone turning them in, and I don't believe they would have wanted to deny their Jewish blood.
Check the link below for more information about Hitler's impact on this family and others like them. Good luck!