1)Montezuma was friendly to Cortes because he believed that they were the Quetzalcoatl, so he decided not to fight them but to welcome them.
2)Sorry but this is too obvious, just copy down the sentence from 'The Conquerors' line 10 to 11.
3)Cortes become nervous he can't understand why Montezuma treated him like a god.
4)Because they think that Cortes is their enemy because Cortes' man killed their men, and they want revenge and their chief is trying to prevent them, so they got angry and killed Montezuma.
Have a nice day! :)
-Vana