Elsa and son Kurt were from Auerbach which you certainly know. They left Bremen for New York on 28 Sept 1926 ("Stuttgart").
The problem is to tell the right Auerbach as there as a few in different parts of Germany.
My first thought was Auerbach im Vogtland, Sachsen/Saxony. An address book of 1925 is online. There are some Schubert entries. Among them is a Kurt.http://digital.slub-dresden.de/fileadmin/data/20394675Z/2039...
You should try to find their immigration record. maybe there is a clue of the State they came from.