wow this is a good point... Hmm im not sure I think maybe naruto gave them BM but he created the rasengans with BSM he just needed them to guide the rasengans
No, not if naruto balanced the senjutsu chakra for each individual. you only turn to stone if the chakra is not balanced with the senjutsu chakra. naruto shows enough chakra control to be able to do this so yeahh
Naruto could have used his tails to smash that "oomph" black thing... but because he wanted to break Obito's will (black rod ) he used his friends as kage bunshi replacements
Just using senjutsu chakra isnt enough to turn you into stone. you need to absorb too much nature energy, and naruto would have balanced it out with kyuubi chakra for the k9.