# Kill all her bulls. Send them down to the place of slaughter

Possible meaning of "bulls" is: soldiers or strong young men.

# Kill all her bulls

"You enemies of Babylon, kill all her bulls". Yahweh speaks to the enemies of Babylon.  

# them ... their

The words "them" and "their" refer to the people of Babylon.

# their day has come—the time for their punishment

"the time for their punishment has come"