Mesh glitches in the game

Hi. Regarding the first issue:
1). Your skirt mesh goes higher than the one you transferred the uv_1 map from. Use a full body outfit ( lingerie, swimsuit ) as a reference instead;
2). Use Nearest face interpolated instead of the default Nearest corner and best matching face normal when transferring the uv_1 map.
Regarding the second issue, the solution is explained here . Please watch everything with the subs turned on to know how to not only fix but to avoid it as well.
Things to keep in mind:
1). The hex code of the color you vertex paint the mesh is important. It controls how sliders and body parameter modifications affect the mesh. So if you want the mesh to be affected like a skintight outfit would be, paint it 00FF00. If not, find the closest ( shape-wise ) maxis outfit and sample the color from it. BUT every nude part of the body should be always painted 00FF00;
2). Sometimes you may get distortions ingame because the imported blend has vertex groups that the original one did not have. In the first case, you transferred weights from the full-body outfit that added many vertex groups that did not exist originally. So if you will ever get certain parts of the outfit flying ingame despite being weight painted the right way, this might be the reason;
3). The backside of faces is not visible ingame, so from the front view your skirt will look like it has nothing in the back. Duplicate these parts and flip the normals.