UE4 mannequin

we are wanting to make a few animations, and tweak a few of the free ones, unfortunately there is no file, or way to export that I know of the UE4 mannequin from UE4 to Blender, I am more asking if you have a model for blender, and or, if there is documentation on animating inside of UE4, otherwise I am at a complete lost on how to make a perfect skeleton for animating.