Some students of the Book of Mormon have wondered how descendants of Joseph were still living in Jerusalem in 600B.C. when most members of the tribes of Ephraim and Manasseh were taken into captivity by the Assyrians about 721 B.C.
A scripture in 2 Chronicles may provide a clue to this problem. This account mentions that in about 941 B.C. Asa, the king of the land, gathered together at Jerusalem all of Judah and Benjamin ‘and the strangers with them out of Ephraim and Manasseh.’ (2 Chronicles 15:9.) These ‘strangers … out of Ephraim and Manasseh’ who were gathered to Jerusalem in approximately 941B.C. may have included the forefathers of Lehi and Ishmael.
(Daniel H. Ludlow, A Companion to Your Study of the Book of Mormon, p. 199)