What is the width of these? Is the length...
What is the width of these? Is the length adjustable so I can use them on all my back country skis?
They come in multiple widths and lengths to fit your skis. If you have skis that are very different in length and width, you'll need more than one pair of skins.
If you want a skin with greater adjustability, the Expedition (http://www.backcountry.com/g3-expedition-climbing-skin) is completely adjustable at the tip in addition to the 10cm at the tail. Width is another issue.