From my experience with this, provided each of your nitrishapes has its skin instance set up correctly and matching with the creation kit, it should work. Invisibility does seem to be entirely down to the skin instance. Having multiple meshes using the same skin instance doesn't seem to be a problem as well. However, things I would check/change in the nif: try using 130 for the body part instead of 131. In your BSlightingshaderproperty, check whether shader flags 1 has sf_skinned ticked. Screenshots of say your nif structure showing skin instance, lightingshaderproperty etc as well as anything from Blender ( export settings etc ) would help - I can't help much with Blender as I'm a Max user.