# You say

These words are added by most versions in order to make it clear that Job is quoting his friends.

# God lays up one's iniquity for his children

"God keeps a record of a person's sins, then he punishes the person's children for those wicked deeds". Job speaks of iniquity as if it were an object that could be stored for later use.

# Let him pay it himself, ... know it

"But I say that he should pay it himself, ... know his guilt'". You may need to make explicit that what the sinner should know is how bad his sins have been.