Who is Daniel and Marty from Chapterhouse: Dune and what is their importance?

Daniel and Marty are enigmatic figures seemingly living on a farm in the U.S. Midwest in the early 20th century, Daniel and Marty end the novel, arguing about whether and why he lets Duncan Idaho and his cohorts escape into untraceable space. They appear to Idaho in dreams at intervals throughout the novel, and he begins to suspect they are Tleilaxu Face Dancers, who operate independently of Masters. Daniel and Marty confirm this, but leave unanswered why they had wanted to capture Idaho and Scytale, and why they find gholas offensive.