Nathaniel,

Reinhold Busch is a retired German physician who is writing a book about
the Rosenthal family of Westfalen, of which my grandmother, and your
great great grandmother Elfriede Rosenthal was a member. Dr. Busch promotes
communication among members of the clan he is studying. 
He asked about you, and when I told him you were a conductor he replied:

Es wäre ja interessant, wenn er (Nathaniel) Kontakt mit seiner Verwandten
 Magdalena Martinic-Jersic aufnehmen würde:
 Sie ist Konzertmeisterin beim Phoenix Symphony Orchestra, 
und ihr Mann Borzivoj ("Boro") leitete das Zagreber Kammerorchester! 
Sie ist Urenkelin von Alma Rosenthal und Albert Neuwahl aus Soest. 
Die e-mail-Adressen müßten Sie haben.

Here's Maggie e-mail address:
"Maggie Martinic" <phxvln@gmail.com>

This is the wikipedia reference:

Maggie Martinic-Jercic - Phoenix Symphony
https://www.phoenixsymphony.org/musicians/magdalena-martinic-jercic
Magdalena Martinic-Jercic, Associate Concertmaster of the Phoenix Symphony, was born in Burlington, VT, and began playing the violin at age 6....

My inference is that Maggie is in her mid- or late fifties,
and has musical connections which she just might want to exploit
on behalf a distant relative.  She's an American and speaks English. 
You might want to take up Dr. Busch's suggestion and introduce
yourself to her by e-mail. I have no opinion,
except that one never knows when lightning might strike.

Jochen