Problems with importing Motion Capture Markers from Blender to Unreal Engine

I’ve tried to import a 3D Mesh of a human model and a motion capture animation from Blender into Unreal Engine. Unfortunately, only the 3D Mesh could be imported correctly. Everytime I try to import my Motion Capture Animation from Blender, which looks like this

I get the following error: Failed to merge bones. No matter if I recalculate the skeleton or not, the Cubes have no animation anymore and get specified as Skeletal Meshes. Furthermore, every single marker is it’s own skeletal mesh with a physics asset linked to it. What should I change in order to import these Marker-Cubes correctly? I don’t want to apply the Motion Capture directly to the Mesh - actually, the markers should be retargeted onto the face of the 3D Mesh. This will be done with the help of a correspondence file, where every Vertex-Marker Mapping is listed. With the help of Voronoi Diagrams I want to calculate the influence of area of one marker, e.g. what area of the face will be moved when the marker is moved. Eventually we want to animate the face with those markers. The Motion Capture markers are used as Bones one can say, but I’m already stuck at importing them.