# During the days of Ahaz ... king of Judah

"When Ahaz ... was king of Judah" This was when the events happened. 

# Rezin ... Pekah ... Remaliah

men's names 

# Rezin ... and Pekah ... went up

"Rezin ... and Pekah ... led their armies up" 

# to war against it

"to war against the people of Jerusalem"