his chakra system was in another dimension much like kamui. so if his body parts gets severed his chakra system is still instact and will keep his organs functioning even if in pieces.
I feel like there are alot of things Kishi has left out, like how did Madara survive and how did Hashirama die? But I dont think those questions are very relevant though.
1- you asked a very difficult question , the only thing I know about jashin that he is ( Saturn ) , I will do some research on this subject ,
If I find something I will tell you .
2- this is an image about saturnulian brotherhood which mean brotherhood of Saturn , you will see the triangle that hidan is wearing