# your enemy ... feed him ... give him a drink ... if you do this, you will heap

All forms of "you" and "your" are singular.

# But "if your enemy is hungry ... his head."

"But the scripture also says, 'If your enemy is hungry ... his head.'" (See Proverbs 25:21)

# feed him

"give him some food"

# you will heap coals of fire on his head

"you will make the person who harmed you feel ashamed about how he has mistreated you"