This photo of a Flore Coenca - probably dating from 1908-1920 is accompanied by a note that says "cousin of M.A." (Moritz Abraham).
This means either Mamo Abraham, or Mamo's wife Lea had a sister who married a Coenca.
Meyer J. Coenca
A calling card sent for Gabrielle's birth from "Mr & Mme Mayer J. Coenca", 49 rue Georges Sorel, Boulogne (the studio Ronya would buy in the 50's or 60's?)
Also, on a 1958 legal document ("L'acte de notoriete pour remplacer l'acte de marriage"), one witness was M. Kohenka, aka Coenca Mayer, businessman born in Constantinople, 31 May 1881.
Assuming this was a relative of Moritz Abraham.
Coenca was a common name... In the list of "Family Names of Rustchuk Jews" in the December 2001 issue of the Etsi publication, the name Cuenca is listed. Was this the same name, the same family?
In the "Bulletin de L'alliance Israelite Universelle, 1er semestre 1884", a Coenca is listed for Constantinople.
If this was the same family, could it also explain the movement of the Abraham brothers from Rustchuk to Constantinople?