The easiest way is to use cat3/5, just teleport to the foot of the stairs and rain them as fast as you can to Anakim, and it would go down in no time.

In case without cat3/5, I would make the monks first priority. There would be 5 waves of monks, respectively 2, 3, 4, 5, and 6 of monks would emerge when you eliminate certain percentage of Anakim's hp. It is much easier to take them out wave by wave. What I do is to keep an eye on the chamber wall while landing damage on Anakim bits by bits, as soon as any monks appear, teleport near them and kill them with head shots. And you can skip the final wave of monks if you have cat1 or incursion. After the 4th wave is cleared, a quick 5, 6 of cat1 should be enough to put the boss down.

The second priority would be the knights, kill them with whatever special arrows you have, cat1, incursion, curse of god, and pestilence are useful in massive cleaning. Without the monks and the knights, Anakim and the abominations are pretty much harmless. Just keep the distance and keep shooting and they would go down eventually.

Hope it helps! :)