AFTON: Chelsea‘s mate
... He has the ability to make himself invisible to attackers, but someone with a strong focus can see through the illusion.
So in other words, if you sit there and stare at him, he'll become visible.
That is possibly the most useless skill since "can see the future if nobody changes their mind."
CORIN: A guard
Officially, Corin‘s primary job in the Volturi is to protect the surviving wives, Sulpicia and Athenodora.
Yes, they are "the wives." They have no function or identity outside being the arm candy of the men.
In reality, she does not protect them so much as soothe them into complacency while other, more physically impressive vampires do the actual job of guarding the wives. The wives are so closely protected that they have become virtual prisoners in Volterra. However, Corin‘s gift keeps them satisfied with life—even happy.
Corin is able to make anyone feel content in his or her circumstances. There is a druglike side effect to her skill, however. A person can become addicted to the feeling she produces, and be unable to feel well without it. Aro has been careful not to expose himself too greatly to Corin, while using Chelsea to keep her tied to the coven. Marcus has always refused to let her relieve his never-easing pain over Didyme‘s death. Caius, on the other hand, frequently uses Corin‘s gift to alleviate his boredom between battles and punishing expeditions.
SANTIAGO: A guard
Like Felix, Santiago is a physical enforcer. He has no psychic gift, only tremendous physical strength.
He likes to show off his big muscles to all visiting ladies.