part of mesh not working with sliders

it was already done but i re-did still same issue :/

Go to a vertex paint mode, change shading to Shaded, you will see that there are parts of the mesh that are painted with white. You need to paint the whole mesh with 00ff00, not just the corset
if my memory serves me well, there was nothing wrong with the uvs in uv_1, and the mesh not morphing is not how the problems with uv_1 manifest themselves 

apologies, that was the upper body from the rig clipping through your mesh.
I also did not check at first, but the area of the body covered by the corset should be deleted and the corset's uvs should go in the freed space. Right now they are partially in the space meant for shoes. Everything is fine with uv_1
That said, none of that would disable morphing. You should try cloning something else that is made of one meshgroup ( like a tank top) and re-import your file there. If won't work, share a package please