1)
Why did Melech Ashur come only against Shomron? Also Chizkiyah rebelled against him (verse 7)!
1.
Malbim: Shomron did not heed Hashem's voice. [Via Hashgachah,] Melech Ashur did not come against Yerushalayim until Chizkiyah's 14th year, at which time Ashur fell.