Where in the bible does it indicate that the 12,000 tribes of Joseph are not all Jews? Jehovah’s Witnesses are saying that the 144,000 (rev ch 7) are also gentiles. Was Joseph’s wife a gentile?
Only two of the tribes of the Israelites were from sons of Joseph. Those were the tribes of Ephraim and Manasseh. Since they are descendants of Abraham through Isaac and Jacob, they are, by definition, Jews. So there is no place in the Bible that would indicate they were not all Jews.
Most of the members of the twelve tribes (except most of the tribe of Judah, and parts of Benjamin and Simeon, and Levi) were taken captive by the Assyrians about 700 years BC. They were scattered throughout much of Asia and lost their identity as Jews. The remainder of the Jews were taken captive by Babylon about a hundred years later, and returned to Jerusalem seventy years later. They, for the most part, kept their ethnic purity as Jews. From an ethnic standpoint most Jews today are descendants of the tribes of Levi, Judah, Benjamin, and Simeon. The tribes of Joseph’s sons and other tribes of Israel effectively ceased to exist 2,600 years ago.
The 144,000 in Revelation 7 and 14 may have included Gentiles, since they represent the martyrs of the church of the first century AD. However, I have made a case from the descriptions of the 144,000 that they represented the Jews who made up the church for almost ten years before the conversion of the first Gentile, Cornelius. (See "What Does the Bible Say About..the 144,000?)
You also ask if Joseph’s wife was a Gentile. Genesis 41:45 indicates that Joseph was married to the daughter of an Egyptian priest. So ethnically she was a Gentile. This would not necessarily make their children Gentiles, however. Clearly they were considered Jews because they were given their father’s inheritance in the division of the land after the conquest of Canaan.