Helmut, please clarify the correct LNAB (last name at birth). You state it should be Hoffmann (two f's and two n's). His father is Hofmann-619 (note only one 'f'). So is it one 'f' or two?
As to the three Frederichs, I would merge them. It says Frederich is an ancestor of U.S. President Franklin D. Roosevelt. Research should be done to see if this is the case. You could detach them from Ferdinand, with a note on the biography as to why he was detached. Once research has been completed, we should know what else to do...