Should we worth noting that Advanced Chakra Natures are not clan based. Only more common in certain clans. Yuki clan, for instance, Haku's clan. Their bloodline limit isn't Ice Release, as people outside of their clan can have it as well, but rather the ice mirror technique and that "Style" of Ice Justu.

Biggest thing that is in favor of what I'm saying is Hashirama Senju. He's the only wood user, no other Senju can do wood release, their KG is rather increased vitality and chakra pool, like the Uzumakis.

It's all to say that you can make anyone from any village, anywhere in the world with any elemental release. Of course, in some places certain genes would be more common. Kekkei Tota's (3 Elemental Advanced Natures, like Dust.) Are incredibly rare and equally powerful as it is rare.

Now, if that's what Partisan and Knight decides to go with, I do not know. But that's the explanation that makes the most sense, in my opinion.