Ill take a stab at the how about the K+G Bros have a little Kyuubi chakra:
They are the sons of the Kyuubi Jinchiriki before Mito. Maybe during childbirth the Kyuubi was released (hence how the leaf knew child birth is a danger for a host) and went wild and Madara ran into it, signed whatever contract to summon the Kyuubi, fought Harashima who made Mito into the Host, etc leading to the current events.
Naruto has the whiskers because his mother was the Kyuubi Jinchiriki - not because he is the host. If he had not become the host maybe his chakra would be tinged with the Kyuubi's aswell, we shall never know in naruto's case. I really cant see it going any other way.
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