
Backing up a bit here: I also have come to believe that Wilfrid Voynich used the bestselling 1906 book, Follies of Science in the Court of Rudolf II as his "primer", or model for creating the VMs. Almost every forgery has a primer, which is the sort of "core" from which a forgery is influenced by, and grows up around. And Voynich was quite familiar with the book. He even said he "knew it by heart", and in his notes, listed at least 19 of the people mentioned in it, and also, in the order they appear in it.
In addition, a great many of the items suspected being represented IN the Voynich... whether the presenter thinks the Voynich real, fake, old, or new... also happen to appear in this book, and often in the skewed form the author, Bolton, presented them. But that is another, much larger subject for another post. This is about the men in the Magic Circle, and who I think they could be.
So I believe the man holding the circular object is probably Kelly, who of course aided John Dee in his skrying attempts. For a great overview of that process, and relationship, I recommend reading Dee's own words on the subject: His diary.
I think it possible that Dee is the man at the top of the circle, facing away. I don't know if a forger would have represented Dee's beard or not, but at least that guy looks older somehow, and we can't see if he has a beard or not. If this guess is correct, the who would be the other two? Well in Bolton, and in the Court, in fact, were both Kepler and Tycho Brahe. And at this time, it was an unfortunate reality that astronomers... as most doctors and (proto-) scientists, were compelled to offer readings for their patrons. It was often expected. Both Kepler and Brahe had to offer some astrological feedback, from their observations, for their patron Rudolf II. And so, I have long speculated (for as usual, speculation is all any of have, relating to virtually any image comparison and identification in the Voynich Ms.) that the men of f57v are, John Dee at 12:00 o'clock, Edward Kelly at 3:00, Tycho Brahe at 6:00, and Kepler at 9:00. Which brings me to an aspect of Mr. Six O'Clock that I have long noted: It appears his nose is clumsily drawn on. It was only last year, however, when looking more closely, that I noted what could be a "strap" drawn, wrapping around the back of the neck, breaking or covering the hair line, which also appears to have a line leading across the left cheek from it:

I've been reluctant to publicly make this observation, because is is, granted, so thin. So it must be taken with a grain of salt, with which it is fully intended. But the thing is that Tycho Brahe famously lost his nose in a duel, when young, and wore a fake nose. This is outlined in Bolton, too, as long as in almost every description of the man written almost everywhere else, and even shown in engravings and sculptures of him. It is one of his defining features, and has been a great curiosity.
But the damning problem with thinking this line a strap, meant to show that the nose was so held on, is this: Brahe didn't use a strap to hold on his nose. He used a glue, or putty, which he would carry around in a small tin with him. He could affix his prosthetic nose if it came loose, or change it out for one of his many replacements... it is said he had as many as 14 of them, and at least one in silver and one in gold. It is believed he was buried with a brass or copper version, though, as verdigris seemed to be apparent on his skull, around the nasal opening, when his tomb was opened in 1901.
So it is dangerous for me to even suggest that this is a strap*, for why would a forger represent a glued on nose, with a strap? It seems unsupportable, and I agree. But nonetheless, I would point out that almost everything in the Voynich is some seemingly skewed version of something that is known elsewhere, often an imaginative and inaccurate representation of something else. Perhaps a forger, trying to evoke Tycho here, was not so specific as we would be today, in either drawing the man, or trying to identify him. And so, maybe, they decided to include an "identifying" strap for the rudely drawn false nose? I at the very least thought it would be interesting to raise the question.
* Two suggestions for this "strap" on the VMS-Net were a tie for his hair, or a fastening for a wig.