Efraim and Menashe were blessed...to be kept by an angel of Abraham Isaac and Jacob (hopefully the angel of truth (tribe of Jehoshua))
Josef was blessed to be kept by the GOD of Abraham Isaac and Jacob.
What is the difference?
Moses could carry the bones on his own and Yehoshua needed a special minyan to do it. Only the people he chose could be successful for this mission, he himself could not do it alone.
Rabbi Nachman COULD bring the Messiah on his own but it was more of a victory that the minyan came into existance!
The minyan we are referring to is the tribe of JOsef. The Na Nach!!!! (only those that want to bring the bones to Mt. Zion)