I need to edit the vertices of about 30 polygons in an equal way, how would I go about this? Alternatively is there some method to just increase the size of a group of polygons 200%?
I believe this is possible using the scale tool:
It might not be enabled by default, so you can turn it on.
Here's a tutorial of how it works:
Failing this you could always do a buffer and then union the output with the original file, although this a bit of a 'dirty fix'