Creating custom pants/body meshes issue.( solved partially )

Hello there, first you need to understand, when people make a CC for sims 4, there are different levels of creation, i see people make items in a bad way, but it somewhat work for them, but when you make something not correctly even if it works, it will get bugged in some situations, and it can be small bugs or big once, i dont give advises on who to make something fast but not good, i dont think people should do it.
so it you want to make a body or lower body item correctly, you got 2 options, you can make everything from start, this will be very hard for you, you will have to learn about vertexes groups, weight, bones, tunning, sims4 xmls and so on, if you want that you should go and start watch tutorials and learn about it.
the other option you have to make fairly fast and easy item correctly is to take the attribute from a default mesh, so if you you starting with a mesh who made from 3 parts or 4 or 5, move these once to the side, create your own mesh, cut your mesh to mach the number of cuts the original mesh had, then take attribute by join every part of your mesh to the part of original mesh who ius in same position, make sure vertex paint and joint all same as the original, and use the same uv position as original. that way you dont have to really understand every part of the proccess and you get a fairly easy good creation.