You didnt prove anything? they cant control the Bijuu within their own body but with their jutsu, unlike the uchiha who have the chakra to control the bijuu, and like i said before the Juubis body would have to be inside of the sage for the eldest to have sharingan. You said the Sharingan was the cursed mark but we have no proof that the juubi had the sharingan you assume that find a spot in the manga where it says they got the juubis eyes, no it says specifically the eldest son received the SAGES eyes his spiritual energy and chakra, Funny how we've never seen a senju jinchuuriki from the leaf only uzumaki which again you assume is senju, Madara does not say naruto is senju itself but that he has the strongest senju will of fire inside him. Kushina is never shown talking about how her body is special she talks about how her chakra is special and if senju were supposed to have the Body of a "jinchuuriki" than Hashirama being the most prominent senju since the younger brother would have been the perfect choice right? Why does everyone steal hashiramas body cells to increase their physical abilities and not Tobiramas. Senju arent the ones meant to be jinchuuriki, we dont know if the juubi contained the sharingan itself because its shown having the Sharinegan in the pictures that might not even be real and could possibly the genjutsu of the sage controlling the juubi and making his eyes take this appearance, and thats not even a metaphor. Metaphorically? Figuratively and from what we've seen from Madara and Sasuke and the uchiha Coup De'tat literally.1) They didn't receive Jubi's eyes. They got a diluted version of Jubi's Sharingan because of genetic mutations.
2) Ironic how the eldest son got Sharingan (Jubi, Madara) and the youngest son got Rikudo's ability to control tailed beast (Rikudo, Hashirama)? It stems from the hatred of Jubi-Rikudo, and has now cursed the Uchiha (Jubi) because they metaphorically are the bad ones.
3) Okay..?
Hashirama didn't become the Jinchuriki of all 9-Bijou simply because he couldn't; Doesn't have enough chakra to sustain all of them. Yes, you need strong chakra in order to suppress Bijou.