Are Pickwick and Otto fictituous?

Pickwick - Herman Sluring - is decribed as a leading resistance worker, but I cannot find any other information about him. There was a guy named Herman Slurink (with final k) but he lived somewhere else (in Zwartlsuis) and he spent most of the war in prison.

About Otto I can say that it is pretty unlikely that he visited the Ten Booms for a short moment, during the war.