Margot's mother, Rosa Ringel, was a victim too
OMG! Rosa Ringel is in the Names database, too. She was the mother of Ze'ev and Margot and was Hermann's sister. She and Margot were both taken in Belgrade, where Rosa's deceased husband David Shattner had come from. I think they were likely living with their Shattner in-laws in Belgrade after fleeing Berlin.
As with Margot, there are testimony forms submitted in Israel by Ze'ev and by Artur Hendel, a Shattner cousin. The forms are handwritten in Hebrew and German so I have not deciphered them. This photo was included with the Ze'ev form.