They're already on Voyager when the battle begins. Also, these nine guys are as competent as a small army. Not to mention experts in their fields, as well as violent sociopaths. Not to mention, due to the fact that the engineer can build teleporters, he'd have a good idea at how the transporter works. And God help the Voyager crew should they discover Voyager's armory.
Now, if this had been the Enterprise, DS9, or the Defiant, well, that's a different story...