1)
Verse 8 already said that Edom rebelled. Why was this repeated?
1.
'Rashi': Since a verse interrupted in between, it was repeated.
2.
Refer to Melachim II, 8:21:1:1-3.
2)
Why did Livnah rebel?
1.
'Rashi' 1 : Livnah was of Yehudah, and on the border with Edom, like it says "he'Arim mi'Ketzei Vnei Yehudah El Gevul Edom?; Livnah (Yehoshua 15:21, 42). When they saw that Edom rebelled, also they rebelled. They are on Edom's border, and helped Edom. They rebelled in Yehoram's days, because "he abandoned Hashem Elokei Avosav." Malbim - they wanted a king who follows Torah.
2.
Refer to Melachim II, 8:21:2:2.
1
Rashi (Melachim II, 8:22) says similarly.
