It is taught that each Jew individual is responsible to follow the 613 mitzvot to the best of his abilities, for each Jew has individual blessings and tests by God.
In his commentary on Ezekiel 37 the Malbim also says that the Messiah ben Joseph will be the leader of the Ten Lost Tribes when they return.
The Messiah ben Joseph will initiate union with Judah, who will be led by the Messiah ben David.
Rather he is presented as the leader of all of Israel.
However some later Jewish sources do explicitly call the Messiah ben Joseph the leader of the Ten Lost Tribes.
However, Matthias Henze suggest that this figure is not a reference to the Messiah ben Joseph who he believes is a later development but rather a pseudonym for the Messiah ben David and that Ephraim is simple a metonym in reference to Israel; Israel Knohl disagrees.