Another underlighted aspect of Farwerck: he was member of the Universal Sufism order of Hazrat Inayat Khan (1882-1972).
In the biography of Khan I had found a reference to “de heer Farwerck” not knowing if this was Franz or his brother, I mentioned this in passing in the biography. There is a Dutch website about the order, particularly in the Netherlands, which has some more information.
Farwerck is mentioned as an “early mureed” (initiate) of the order. He became a member in 1921 and in that and the following year he was secretary of the Dutch branch of the order. He was followed up by Eqbal Dawla van Goens van Beyma in 1922.
On the website is some information about Farwerck (mostly from Wikipedia) and there are some familiar names, such as Anne Kerdijk (wife of Stephan Schlesinger who designed the cover of Farwerck’s first book and his Masonic ex libris, Kerdijk was one of the first Dutch co-Masons). There is also the couple Van Meerwijk who were also fellow Masons (they left Le Droit Humain in 1940 together with Willy Farwerck). The couple Van Ginkel (early co-Masons, Van Ginkel initiated Farwerck in 1911) were also active here. We also find Nico Kluwer who would publish Farwerck’s final book after Farwerck had died.
The biography of Inayat Khan has more names. Baron van Tuyll van Serooskerken (chairman of the first National Executive Committee) who was married to “my mureed Miss Willebeek Le Mair”. Sakina Furnee and a mr. Wegelin.
I don’t know how long Farwerck was a member, but this ‘neo-Sufi order’ is certainly the most ‘spiritual’ interest of his that I have found so far.