Why do you think they were able to tell Mr. Frank is able to stay calm during his family’s final moments in hiding?

I think they were able to tell Mr.Frank is able to stay calm during his family's final moments in hiding is because he knew that once they get caught they could've been separated and bad things could happen to them since when he got off the train to return to Amsterdam, he hears his wife died. When he goes to meet Miep and Mr.Kraler, he find out that Margot and Anne have also died which made him quite sad but, he had a feeling this would have happened sooner or later.

you need to include the text. we have no idea what you are referring to