Looking lovely Wesley! Have you tried when importing, instead of selecting 'normalmap' select 'uncompressed_normalmap' ? its named something similar to that.
Do you mean that you have a double sided piece of clothing, and that the weights on one side are different than the back side? quickest way to solve that which I know if is to select by vertex and apply weights by flood fill. Then you can smooth it afterwards if needed. This way you can make a vertex selection in wireframe…