Hi,
This is indeed a weight issue.
You can already test it in blender by applying a modifier type : Armature with the rig as source.
Then make the rig visible and selectable so that you can select the joints to rotate them around and see how the model behaves :
![](https://img4.hostingpics.net/pics/798893splitskirt.jpg)
Now the problem is more how to fix that. You can try this
tutorial. I advise you to subdivide the reference mesh as to have a better match when transferring.
Unfortunately I don't think that will fix the issue. The main reason is that EA doesn't create meshes with existing body parts under the clothes. Therefore all the weight transfer you can do will not take into consideration the legs under the clothes. The result is basically the issue you are facing.
I have created some skirts with the legs still visible under the skirts and have faced this issue. The only I found was to manually modify the weight painting as to fix it myself. The problem is that the behavior in Blender is not quite exactly the same as in the game, or probably more that the game rotates way more bones for normal movements as I usually move to tests things around in Blender.
Hopefully after the weight transfer you will only need some small adjustments. From how the dress doesn't fit the waist and seem to float around, you clearly at least need to do the transfer and then check it out. (I really don't like weight painting.. it's really hard to get right when done manually)
Bon courage.
PS : You can isolate the uv_1 by modifying the legs/tights/waist sliders and see how the skirt behaves. From the form of your Uv_1 it is not perfect but should mainly go along with the sliders, the issues created by it should mainly be visible when reaching the min and max of the sliders.