I think you're conflating several batshit insane religious nutjob theories. I've heard some Mormons for example suggest that black people suffered from slavery because they were descended from Cam, Noah's youngest son who was cursed for ridiculing Noah who was the one who got drunk and naked in his tent.
The part about the lost tribes of Israel I've seen comes from certain evangelical groups as a justification for America's westward expansion (and the death and destruction for American Indians that came with it). Basically Jacob, the ancestor of all the Isrealites, promised his favorite son Joseph that his own sons, Manassas and Ephraim, would give rise to great nations of their own. Flash forward a couple thousand years and somehow these two lost tribes of Israel go on to found England and another group of them breaks away and founds a little country called the United States of America. So basically according these groups, WASPS (White Anglo-Saxon Protestants) were destined for greatness by God because they are a lost tribe of Israel. This was a hugely mind-blowing idea when I first heard it at age twelve.
The point of all this nostalgia for a more superstitious time is that the same people who are coming up with all these crazy ideas are the same people who are trying to make Creationism sound scientific. And a lot of them are perfectly nice, friendly people so it's not like you want to (or even can if they're family) cut them out of your life. Eventually mocking them with tales of Flying Spaghetti Monsters gets tiring and you just find yourself talking about sports.....