Frogs take time to summon. One amaterasu will end the frog and the genjutsu. Sasuke can see chakra from underground now it wont come as surprise. This trick doesnt work with ribcage thou, and KCM has nothing to destroy it, FRS are easily countered by enton or fire jutsu.
No they don't, Jiraiya was gathering natural energy while he was running and summoned them as he went SM, Ma toad uses natural energy and was summoning Naruto, Pa toad, 3 giant toads and Gamagichi. Naruto summoned toads fast himself. How is Sasuke going to use Amaterasu when he's paralyzed and Naruto having the toads fused to him, he can react, and use of clones.
Sasuke can't just see chakra underground, he has to activate that ability, meaning he has to feel like he needs to use it. He activated it during the fight against Kabuto as shown here:
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. Yes it works with the Rib cage, 1 hand holds the cage and 1 grabs Sasuke and pull him. Naruto can use many chakra arms plus clones. As for the enton and fire jutsus, FRS would cut thru them, they have to be on FRS level and be in a condense form. If it's just a Enton wall then it's going to cut thru it as
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nad it cutting thru Juubi's tails
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and
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But even then, Naruto can just use Chou FRS as well as the bigger one he seems t be making right now in the chapter.