Unless you were an archivist for the Third Reich, there is no such thing as "part Jewish". A person is either is or is not. In Jewish law, if Brahms' father's mother was Jewish, then Brahms' father was Jewish. And if Brahms' father was Jewish but his mother was not, then Brahms himself was not.
The cast of Robert Schumann - Clara Wieck - Johannes Brahms - 2006 includes: Norbert Funken as Arzt Elsa Hanewinkel as Clara Schumann Rita Lilienbecker as Magd Dennis Lilienbecker as Reiter Sebastian Mirow as Johannes Brahms Eline Sickmann as Kind Clemens Wallmeier as Pfleger