ShouldBeStudying: I have not worked with nif files in a while; however, I know of some ways to get you somewhat started in bringing models to Skyrim/Skyrim SE.
https://github.com/niftools/blender_niftools_addon (There are a few blender plugins that you can use to convert files into the nif format)
https://www.nexusmods.com/skyrimspecialedition/mods/4089?tab=files&file_id=157335 (This allows you to make the file ready for Skyrim or Skyrim SE)
https://www.nexusmods.com/skyrimspecialedition/mods/201 (I believe outfit studio also allows for conversions)
I apologize if this is not exactly what you are looking for. This is all I know... Good luck!
Dramatic Descriptions
https://github.com/niftools/blender_niftools_addon (There are a few blender plugins that you can use to convert files into the nif format)
https://www.nexusmods.com/skyrimspecialedition/mods/4089?tab=files&file_id=157335 (This allows you to make the file ready for Skyrim or Skyrim SE)
https://www.nexusmods.com/skyrimspecialedition/mods/201 (I believe outfit studio also allows for conversions)
I apologize if this is not exactly what you are looking for. This is all I know... Good luck!