Everything that is visible in the pictures, is made in Blender and exported/imported as FBX, without changing anything, except giving a glass shader from the Unreal Market to the Windows.
I also discovered, that when i take the Boards that make up the Floor (and being reflected properly) and move them above the camera, they suddenly get reflected in the same weird way. A flat Cube with a wood Material gets reflected properly tho, despite being in the same position.