And late Princess Cristina's children are just Guillermo.
The difference was that no Royal Decree was needed, no surname established, because Princess Christina was leaving the Royal House.
The same did count for Princess Irene. She happened to be married with a royal herself but regarding names in exactly the same situation.
Leaves Prince Friso. As (in 2004) children automatically inherit the paternal surname and eventual titles, a Royal Decree was needed to establish the surname of his eventual children.
When Pieter-Christiaan and Floris left the Royal House no Royal Decrees were needed either as their title
prins van Oranje-Nassau was for life only and not hereditary. Their eventual children automatically became
Van Vollenhoven.
But in the meantime we have four gentlemen with the style
prins van Oranje-Nassau, Van Vollenhoven, four in-laws with the style
prinses van Oranje-Nassau, Van Vollenhoven, one gentleman with the hereditary title and predicate
graaf van Oranje-Nassau, jonkheer van Amsberg and four ladies with the personal and not hereditary title and predicate
gravin van Oranje-Nassau, jonkvrouw van Amsberg. That makes 13 Van Oranje-Nassaus outside the Royal House and I think, by hindsight, it better could have been the Rosenborg, Frederiksborg, Monpezat way, a clear distance from the Royal House by strictly using
Van Oranje-Nassau for the Royal House only.