Checking if any new material was added to newspaper archives I found two things. One is a newspaper article with a photo that shows Kees-Jan Farwerck, one of the sons of Willy Farwerck and Johanna Borrius.
The other finding is somewhat related, because it seems to imply that “Mrs. Farwerck” may not be Kees-Jan’s wife Theodore Hoolboom.
I’ve updated the “one generation further“, added a little text to “Who was Mrs. Farwerck?” and added the text “Beethovenlaan 11“.