Hi,
I will try and help.
I imported my plane successfully as SKEL mesh and I could even animate it using its bones.
In Blender I did NOT join all objects.
I treated each one separately and weight painted each object to the same armature.
I made sure though that transformation for each object was applied in Blender and that the point of origin is exactly the same for each object.
Then when you are done weight painting (skinning or rigging), you select all and export as .fbx.
All those object go out in one .fbx (don’t join then).
When you import into U4 make sure you create a folder first so all your objects come into it and it will be easy to select them.
Then if you selected the right skeleton, just select all the objects in your folder in your outliner and drag them onto the map.
They should all fall into place, just as you had them in Blender. 