Approach the gathering from the front gate. There’s a watchtower point near the stage where Remy is giving a sermon to his equally disgusting herd. Take the mountain road, not the hillside stairs. As long as you approach with stealth, you should be able to take out the sniper in the watchtower and take up the position there. When ready, prioritize disabling Remy then eliminate his remaining men as you see fit. Throw grenades or molotovs to the crowd, including the non-hostiles since they equally deserve what is coming to them.