# They have returned to the iniquities of their earliest ancestors

"They have returned to committing the same iniquities that their earliest ancestors committed" 

# walked after

"followed after"

# The house of Israel

"The kingdom of Israel". See Jeremiah 3:18. 

# the house of Judah

"the kingdom of Judah". This includes the descendants of Judah and Benjamin. See Jeremiah 3:18.