well...dont know about the kin gin bros,but naruto had the whisker marks since he was born.Not from after he gained the ninetails.
The point was that anyone that harbors or get harbored by a tailed beast gets similiar traits I.e naruto, kin and gin brothers.
The only thing the same about them is the sharp teeth. Alot of Kiragukure ninja do it. Kisame really has those traits of a fish.
Kisame should revive himself and kill you..
He is Kishi's imagination, that would answer your question.
It's possible because Three tails was roaming in the Hidden mist.
Hidan is human, He gained immortality through his religion ...The big question is who Jashin, and how does he grant people immortality.
Akamaru is still a kid, Like most other ninja summonings, he'll be able to talk soon
No idea what samehada is and how it was made, i'd guess sealing a creature into a weapon... shark maybe
The blue skin thing must be paint or dye or something, Maybe a Hidden mist thing for a particular clan... Most mist nin sharpen their teeth, so maybe where kisame and the last samehada come from, they dye their skin blue
How would it be paint? He is always in the water. The most plausbile answer is that he's been inside the three tails. He has all the signs. Tailed beast chakra and fish like qualities. It just screams bijuu.