The quest has a minor variation depending on who holds the crossing. If the Brotherhood does, a member will approach you pleading for help (you can attack to claim the settlement) and later you will witness Raetommon killing Ring-Dropper Ceratha in the Moonrise Market. You also won't fight any Brotherhood members until the last group of four. Otherwise:
Straightforward (if you choose to remain with the Chorus). Sweep through the Crossing and kill the Bronze Brotherhood members. There are two groups in each district, for a total of about 12 fighters (excluding the ones who attack you at the exit from the oldwalls). Saber, the commander on the attack, is in the Moonrise district, ground level.