Points Of View And Thoughts

Poul Anderson verbalizes and italicizes the thoughts of a viewpoint character, e.g., Manse Everard of the Time Patrol, while that viewpoint character converses with other characters in the usual way in unitalicized dialogue enclosed within inverted commas. I always found this perfectly clear although one fellow pupil at boarding school had to ask me, "Who is saying this?" while pointing at one of Everard's italicized thoughts. In Dune, Frank Herbert verbalizes and italicizes the thoughts of two characters, the Baron and his nephew, while those two characters are conversing with each other. Most authors accept that you just cannot do this. What would be a more appropriate or elegant way to do what Herbert tries to do? Two parallel columns, the first presenting the dialogue plus the Baron's thoughts, the second presenting the same dialogue but with the nephew's thoughts? That sounds cumbersome but Herbert's existing texts just come over as wrong at least to some readers. There must be some way to resolve this.