7 - For many, maybe even all models, you'll notice that vertexes and by extension triangles are laid right on top of eachother, though generally, only for triangles that are mirror images of each other. These vertexes, pointed out by the arrow, are actually 2 sets of nearly identical triangles, namely the left and right side of the bottom of the thief character's shirt. (The white cloth that hangs out under her corset, almost like a skirt). The front and the back of this area are the rectangle-ish shape below the one pointed out by the arrow, and the one below the bright gray area. All four of these, are mapped to roughly the same part of the texture, and as such, the place where they touch is practically invisible.
8 - What you see here, is that as I said, vertexes in that area, are actually 2 identical sets of vertexes, from either side of the bottom of the shirt, left and right. If you want to move one, but not the other, the most straightforward way, is to click one of the vertexes, "Select Connected" via a right click option, and then use either click and drag, or Alt+S to move them apart. As you can see, while these vertexes are right on top of each other in the UV map, they aren't actually "connected", since they are on opposite sides of the model.
If you want to move them both, which in most cases is likely the way to go, you can simply box select the entire shape and then Alt+S or click and drag them together.
Finally, since sometimes these duplicates are going to be in crowded places like the bright gray square, if you want to move them together, you can also Click->Select Connected->Alt+S move them to a precise spot by translating their coordinates by say 6 to the right in the X axis, then repeat it for the other set of triangles, after which they will be once again right on top of each other, except by 3 texture widths to the right.
So then, now that you know all this, what else is there?
If you, for example, want to add more variety to a texture, you could do one of the following:
a) Select every vertex group outside of the bright gray area, and use Alt+S on them with multiples of 2, until you move them inside of the bright gray area. This will show you what parts of the texture are actually not used right now, if any. At this point, you can use a .dds editor like GIMP to fill in that part of the texture with whatever you want, and move/scale/rotate the triangles until they fit into that part of the image.
In the Female Thief's example, you could for example give the bottom of the shirt a new texture to spice it up, and put that texture in the bottom left corner, as no other part of the model uses the bottom left corner, and no part of the skirt is much bigger than that blank area there.
b) If you don't mind the rest of the model's textures losing a bit of resolution in-game, you could move everything into the bright gray area as before, and then select them all and scale them horizontally or vertically by some amount.
If for example, you scale them horizontally, along the X axis by 0.8, that will mean that they now are only 80% as thick as they were before. At this point, you can Alt+S (or if you're brave, click and draw) them to one side of the bright gray square.
Now you have 20% of the entire texture unused. In GIMP or your choice of software, scale the entire texture the same way, shrinking it to 80% horizontally, and moving it to the same side you moved the vertexes inside the bright gray square.
You can now pain whatever new texture you want into that 20%, and then move the vertex group you wanted to use that new texture into that part of the image.
There's also the issue of figuring out what part of the body some of these vertex groups represent. While some are going to be obvious, such as textures for a medalion making it obvious it's textures for the character's neck in this case, or hand shaped vertex groups being for hands, other times it may be hard to figure out which triangles appear where on the body.
A quick and dirty way, is to simply put different colored X-es on the actual .dds file in various places, and then seeing in-game which color X appears where.
Naturally, this is a bit hacky, and obviously not the best way to do it. If you figure out a way to reliably get the same or better results in Blender, or some other piece of software, I'm sure people would be grateful to know!
But for now, this is just a dirty deed done dirt cheap kind of way to do it.
Also, one last thing to remember: While I suggested moving everything into the bright gray area, it's tidier to then move the vertex groups back out around it using the Alt+S multiples of 2 method. It might make your life easier later on, while trying to move around the vertexes again, or for someone else who might want to use your .nif files.