Both his father, Paul, and brother Edgar had careers as Opera singers.
Grandfather, Dr. Ferdinand Von Hiller, Kapellmeister, cut a locket of hair from Ludwig Van Beethoven's head on March 27, 1827 (the day after he died). At the time, 15 year old Ferdinand was a student of Beethoven's friend Johann Hummel. Ferdinand was also friends with Chopin, Liszt, Wagner and Mendelssohn.
His half brother Felix was also a singer/actor.
The family's name was actually Hildesheim but was changed by Erwin's great-grandfather Isaac to hide their Jewish identity as anti-Semitism rose in Europe (early 1800s).