GOD said, and Jacob prophesied, that Israel would become a multitude of nations (peoples).
And God said unto him, Thy name is Jacob: thy name shall not be called any more Jacob, but Israel shall be thy name: and he called his name Israel. And God said unto him, I am God Almighty: be fruitful and multiply; a nation and a company of nations shall be of thee, and kings shall come out of thy loins; Genesis 35:10-11
And [Jacob] his father refused, and said, I know it, my son, I know it: [Mannasseh] also shall become a people, and he also shall be great: but truly his younger brother [Ephraim] shall be greater than he, and his seed shall become a multitude of nations. Genesis 48:19
Israel was called Ephraim after it split from Judah because Ephraim received the rights of the firstborn and inherited the promises of GOD. When Jacob said his seed would become a multitude of nations, he meant the spiritual seed who would inherit the rights of the firstborn and the promises, who is Christ, whose seed has become many nations (peoples). The genealogy of GOD's people is, and always has been, according to faith.