When did the Kin/Gin Brothers get their Nine-Tails power?
According to this Naruto Wiki page (second and third paragraphs), the brothers were swallowed by Kurama before the battle between Hashirama and Madara took place (the battle after Madara's desertion from Konoha, when he used the Sharingan to tame Kurama).
This would mean they were swallowed before Kurama was ever sealed inside any Uzumaki.  


Chapter 529, page 3


  Now, we also know that the Kin/Gin brothers were at the same time as the second Hokage, Tobirama. Given that they were the ones who killed him.


Although this is true, I think Tobirama and Hashirama are almost the same age, which would mean Kinkaku and Ginkaku's age is somewhere around both Senju brothers.



From what I understand, the timeline would go something like this (not sure about how much time between each "step"):  


Founding of Konoha;  
Founding of Kumo;  
Kinkaku and Ginkaku get swallowed, when sent to capture Kurama;  
Madara deserts and attacks Konoha, using Kurama;  
Hashirama wins the battle, and Uzumaki Mito seals Kuruma inside of her.