Very interesting background. I think one thing everybody ignores is that the grandmother must also have been pretty left-wing, despite being a bank officer. The entire family reminds me of the families of the red diaper babies I grew up with in New York (where, btw, they even went to a school known as the Little Red Schoolhouse), except that most of the New York RDBs were Jewish and their families, who were by now well off, had gotten into heavy duty Marxism through labor union organizing. However, there was also a Unitarian component that was very much like the Dunham family.
The Unitarians went to a very well-known Unitarian “church” in the Village, and the Jews went to the Ethical Culture Society on the Upper West Side. Neither of these institutions had anything to do with real Christianity or Judaism. As the RDBs grew older, they threw aside even this pretense, and burst out as violent Marxists in full flower in 1968.