I have several cosmetics mods like Improved Facial Texures, Natural Faces & smooth EGT faces that make my vanilla characters & NPCs look great, but for customs races and for companions especialy (mostly my CM Partner Companion Kaleah) I dont know where to place the textures files to make them look as good as the vanilla races, so any help is more than welcome

Depends on how the particular race/companion is set up. Check its folder structure and naming of the head textures and mimic it (back up the originals first).

Kaleah is a mystic elf, and she has a separate Mystic elf folder for textures...ah I see your point thanks!