I could've sworn they were completely different situations but there's also a chance you're right. Can you link us to a page that agrees with that by any chance?
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Here are 3 links that would prove that they were apparently 2 different situations. It does say that because of their names that Kinkaku MAY have been their leader at some point. But it also says that during a peace confrence between the Cloud and the Leaf, that the brothers staged a coup de teat against the 2nd Raikage and left Tobirama near death. Not a pair I would trust as a Raikage if they had betrayed me before.
But anywho, there it is. Didn't say specifically that the brothers killed Tobirama. Didn't say that Kinkaku was even with the 20 cloud that killed him, much less his brother. So, there is where I got my information from. Please feel free to correct me if I am wrong.