When surnames started to become set in about the 13th century, they were based on one of 4 things - the father's name (eg Johnson or Thompson), an occupation (eg Smith or Thatcher), a nickname (eg Short, Black) or a location.
The location can indicate a village or town that a person came from (usually indicates that they have moved away from there), (e.g. Mansfield, Ticehurst), or describe the area within the village where they lived (E.g. Moore, Meadows), or in the case of Wenban/Wenbourne indicate the name of the property where they lived.
So, the cronology would be something like this.
Once upon a time a Saxon named Waenna lived by a stream, and perhaps "owned" the land around that stream, hence it became known as Waenna's Bourne. The name stuck and a later farmhouse (and the associated farm) became knowns as Waneburn and eventually Wenbornes. Later the people living there became known by the fact that they lived there (such as Gilbert de Waneburn and Hugo de Waneburn who paid tax in 1295. In 1328 Gilbert is called Gilbert de Weneburn and by 1370 (at least) the "de" meaning "of" gets dropped, and we find Simon Weneborne, Richard Weneborne and Walter Weneborne, and by 1389 we find John Wenbourne. In 1426 we specifically get "John Wenborne of Wadhurst".
So the name existed as a surname before Robert Whitfield came to Wadhurst, which is generally beleived to have been about the end of the 15th Century. I know that Alfred Wace, in his book "The History of Wadhurst" says that Whitfield named the property Wenbans, but I believe this to be untrue, as we have seen the name was in existence before his ownership of the property. I also beleive it was owned before him by "Wenborne of Wenbans", the first husband of Kathleen, and that it was through her that he inherited the property.