B'nei Zilpah are of an ancient origin. In the Hebrew migratory tradition begun more than two millennia ago, a Jewish remnant migrated into Europe ~ from Iceland to the Russian Far East ~ with many European Asherites migrating back to their tribal allocations in Israel, Sidon and Tyre, as well as Slavic Gadites South and East of the Dead Sea and the Jordan River.
B'nei Bilhah are of an ancient origin. In the Hebrew migratory tradition begun more than two millennia ago, a Jewish remnant migrated into Africa with many Danites from Northeast Africa migrating back to their tribal allocations in Israel, such as Tel Aviv, besides emerging Naphtalite communities throughout Mainland Africa, including observant islanders from Haiti and Jamaica, Madagascar, to Papua New Guinea, as well as a Mixed Multitude comprising the African Diaspora from the United States of America settling near the Sea of Galilee.
user6591: I'm pretty sure the Tanchuma mentions the brothers in Egypt asking Bilha's advise how to deal with Yosef after Yaakov passed away.
