We left two of the twins up. We then proceeded to kill everything else, on the death of the last lord/lady, Vulak will spawn. We engaged him, and had 2 knights intercept the remaining twins when they rushed to Vulak aid. We had the knights kite them in a wide circle around the lava pit while the rest of the raid did the event. It wasn't hard, I kited one of them - they run super slow. The most difficult part is not over-running them and causing them to drop agro, and the slippery parts of the path that can cause you to fall into the lava pit if you aren't careful.
Once Vulak dies, single pull in each twin one at a time and kill.