I will concede one point, that gentiles indeed can become "Jews", but only because it doesn't imply a Jewish bloodline, which is what I meant. It only confers "Jewishness" in the religious sense.
I have just learned that there is no identifiable Jewish bloodline, which explains why Jews insist that there are no tribal bloodlines that can identify the other tribes, and therefore they are free to deem descendants of the other tribes "Jews" as well.
The problem with this is that the other tribes do retain their tribal identity mainly within the WASP countries of northern Europe as well as the English-speaking nations of the world. God promised that "not a seed would fall to earth" during the post-Assyrian captivity sojourning of those tribes of the Northern Kingdom, the 'house of Israel'.