everything you say is mute due to the fact OP granted full knowledge. therefore;
1. Both the hokage will go for the decapitation immediately due to complete knowledge
2. Kisame has to swipe his sword past both men on order to steal their chakra
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Not happening as both of them are tiers faster than kisame. In terms of movements and reactions. They easily teleport away and avoid that hoodwink
Touching kisame doesnt make them lose chakra. Samehada does, and that has been countered above. Factually.
Kisame cannot counter FTG's speed. If minato does this and teleports instantly
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whats he gonna do? He gets marked, and beheaded.
waterdome is countered by gamabunta who escapes before kisame can harm him. on top of that, tobirama and minato each make clones of their own and spread out, allowing them to escape. and finally waterdome is not practical due to itachi being here.