Mates of the Volturi leaders. The wives are also powerful figures of authority and core members of the coven, but they only go on trials with their husbands on behalf of extremely important matters, not leaving their tower in Volterra but once every few centuries. Since then, the wives became virtual prisoners in their tower. To keep them happy and content, Aro sent Corin to keep them company, using her power of being able to provide people with an addictive contentment. The wives are well protected in their tower. Aro's sister and Marcus's wife, Didyme, was one of the core members before she was killed. If the wives are taken to witness the coven's actions, they are usually very heavily guarded as well (from http://twilightsaga.wikia.com/wiki/Volturi).
Sulpicia - Aro's Wife
Sulpicia: Aro's mate. Aro created her, because he wanted to make a mate instead of finding one in order to avoid complications. She is completely loyal to him - @TheSulpiciaV
Athenodora - Caius' Wife
Athenodora: Caius's mate. She has been part of the coven since before they rose to power - @DoraOfVolterra
Didyme - Marcus' Late Wife
Didyme was Marcus' wife and sister to Aro. Without Marcus' knowledge, Aro killed his sister to make certain that Marcus remains in the Volturi. She has the ability to make someone extremely happy.
The Volturi secretaries are both human. The first and original secretary that was in both book and movie was Gianna. However, in Breaking Dawn Part One 'the movie', an additional character that was not mentioned in the book was added as the secretary (Bianca). They were both killed by the Volturi.
Gianna Di Morelli
Gianna: She was the Volturi's human secretary who appeared only in New Moon. She had hoped to become a vampire, but in the end the Volturi found her nothing more valuable than her blood - @DivineGianna
Bianca: She was the Volturi's human secretary after Gianna's disposal, and only appeared at the end of the first Breaking Dawn movie. Because of her bad spelling and grammar, Aro had her disposed of.