The Volturi are essentially a kind of royal vampire family. It is the biggest coven in the world when including the Volturi leaders and the Guard. They are responsible for making sure that the existence of vampires remains a secret. The Volturi leaders, mainly Aro, are also old friends of Carlisle's. Their base is in Volterra, Italy.
There is no specific group known as the "voultrie." It is possible that there may be a misspelling or a reference to something not widely recognized. If you can provide more context or details, I may be able to assist further.