From looking at the Banana documentation it looks like it should be able to do what you want, provided that your computer can handle the amount of data without too many drop-outs, but be assured this is a difficult task for one computer. The "professional" way to handle this would be to use two conventional mics, a computer for the Skype, a mixing desk capable of routing all the signals where you need them, and a separate recording device such as a stand-alone 4 track recorder or a second computer. If your computer is reasonably modern / powerful, the Banana route with USB mics will be a lot less costly, if you can get it to work.
I'm not able to help you with Banana as I've never used it, and I don't use Windows. Fortunately the documentation for Banana looks pretty good. Plenty for you to read over the weekend http://vb-audio.pagesperso-orange.fr/Vo ... Manual.pdfhttp://vb-audio.pagesperso-orange.fr/Vo ... Manual.pdf
Let us know how you get on, and good luck.