separate the staff delete the extra meshes variation. then create a dummy object with the exact same name as the staff and attach to the hand boneit in lieu of the staff. This way you might be able to use the invisible dummy as a socket and then attach the actual staff object to it. This way the rig would be the same ( naming etc and joint count).
Unity is easier to use in the way it handles fbx. Basically you could just import one fbx containing a lof of different meshes skinned or static and just activate or deactivate them in editor or even at run time. In unreal there is a lot of extra steps to do such simple things…
Hope this helps.