1)
Here it says that that Retzin and Pekach ben Remalyahu could not fight [against Achaz]. In Divrei ha'Yamim II, 28:5,6 it says that they struck Achaz and killed 120,000 from Yehudah in one day!
1.
Malbim (here and Divrei ha'Yamim II, 28:5): From Yeshayah 7:1-6 it seems that when Retzin and Pekach ben Remalyahu each came by himself, he could not fight Yerushalayim, but they ravaged other cities of Yehudah. When they joined together, they were unable [to depose Achaz and make Ben Tav'al king].
