Could you provide the source of the files? To make animations.
For example I opened https://github.com/fyrox-book/fyrox-book.github.io/blob/main/src/code/tutorials/rpg/data/models/paladin/paladin.fbx in blender and it seems that the "bones" are not connected to the 3D model.
Not sure if maybe that file is the source but you need some app or something.