Tableau vivants are set stage pieces, with every person standing stock still and usually at least partially NAKED. The were common place in the late 19th and early part of the 20th centuries. Many times, they were recreations of famous paintings, but not always and were used in the ZIGFIELD FOLLIES and THE FOLLIES BERGERE.
So the author was trying to reduce Roberts and his family to mere stage props. Well, it's not everyday that you get to see a stage prop being elevated to the highest court in the land.
I think that I remember reading about that in "Little Women". Or maybe it was "Jo's Boys". It was (in the 19th century) a respectable opportunity for respectable young women to "display" themselves in some romantic scene(clothed of course)from a painting,or a famous historical scene,or some such.
LOL! Not in Little Women they weren't!