I'm almost completely positive that Evan Tolliver isn't a Vesper. It's common sense. I mean he's helping Cahills, so I don't think he is their enemy.
Damien Vesper
Vesper Four, the Vesper Scientist is Sandy Bancroft.
Sinead
Vesper Five, the Vesper Spymaster, is Interpol Agent Luna Amato.
Vesper One is the main antagonist in "The 39 Clues" series. Initially, their identity is unknown to the Cahill family members who are searching for the 39 Clues, but Vesper One's goal is to find all 39 Clues for their own mysterious agenda. Throughout the series, Vesper One's true identity and motives are gradually revealed.
suspected vesper hideout
vesper target sunk
Vesper two
vesper two
vesper target sunk
suspected vesper hideout
suspected vesper hideout