It's all one target.. all share the same vision. It's 6 bodies. Not 6 minds. In case you didn't know, unlike ninjutsu, genjutsu hits the mind not the target itself. And since it's Nagato controlling the bodies with his mind.. once he's caught in genjutsu it's over. No proof he can escape tsukyomi or that visual genjutsu wont work. You say Itachi didn't use it on Nagato but you seem to forget that it was edo nagato so would've been useless since Kabuto could just break the genjutsu nagato was in. Itachi could shoot amaterasus on different targets all at once and none of the pains nor nagato is fast enough to dodge amaterasu (also pain doesnt have the reflexes to shinra tensei the amatarasu before it hits him and burns him alive). Itachi has genjutsu that Pain has no defense against once caught and Itachi is a master mind at capturing people with it, not to mention Itachi also has the best susanoo. The ultimate defense which has the mirror to defend against anything and the sword to seal anything almost instantly. There's no way a non edo Pain or Nagato is winning this man get real... Not to mention, Itachi is also a genius like no other. You honestly think he'll be bested by nagato with all his tools?