In regards to the Willoughby stuff posted -- the closest things I can think of to that in regards to the multiple low-level centers are the mesovortices exhibited in the centers of very strong hurricanes. Often, around the larger center, you can see 3-8 small vortices rotating around the larger center. Occasionally, this phenomenon occurs near an eyewall replacement cycle, but it is not necessarily a precursor to one (meaning what I am trying to say is that the two really aren't coorelated). Isabel exhibited this, as did Frances and Ivan.

In regards to the paper posted about binary interaction of tropical cyclones -- if I'm not mistaken, that is more the interaction between two separate tropical cyclones instead of two distinct vortices within the same circulation envelope/system. There's only a small amount of research on the latter problem. Whenever I think of this scenario, though, I'm reminded of a starfish pattern of vortices rotating in tandem with each other in the central Atlantic one year about 5-6 years ago. Really weird to see, but pretty interesting. And it does occur more than it may seem.