I personally feel the two brothers are uzumaki for the fact they survived in foxes stomach without dying and the fact they can hold on to the so6p's weapons without there chakra depleting so much.....
The Uchiha and the Senju are also descendants of the Leaf so to just say they are Uzumaki is odd. The likelihood is that they aren't Uzumaki because their village was still in existence at that point and the surviving Uzumaki hadn't scattered yet.
@NLee - The reasons I think Kin-Gin are lame are:
1. They were never mentioned before. Not even a mention of the guys who almost killed the 2nd Hokage and their strange abilities...seems odd since we've heard of everyone else who's been resurrected. There was a Kinkaku Force mentioned, but no specific mention of them.
2. We got a very quick abbreviated backstory on them. That's not a huge issue, but mixed with number 3 it is.
3. They were gone as quickly as they arrived. 5 manga chapters, that's it. They showed up and in 5 manga chapters they're gone. Back into their obscurity, maybe without even being mentioned again.
4. They not only absorbed some of the 9 tails chakra they also had their appearance transformed (the whiskers marks on their cheeks like Naruto)
5. Their main weapon attack involves the word you've said most in your life.