Something i didn't understand....

i want to ask few things:

though it is novel based story,and characters are fictitious but i don't get something.what was the story centered at.

when they were all midnight's children,and they knew everything then how did Shiva didn't know that he was a changed baby.

how did Shiva became the army guy.

i haven't read the novel and just saw the film and don't know there is a notion in my head that there was something wrong in the whole story line.The plot must be altered,as it was too confusing.

Soha was singing song of Noor Jahan "mujse pehli se mohabbat" in a theater.was she playing role of Noor Jahan?