If you're tired of going in fair and square, try this:
https://www.youtube.com/watch?v=cU7WUePfhPQ
If you just want tips:
https://www.youtube.com/watch?v=m2wRQcrHZec&list=PLOjGXMeTrh2heFtd-_s_4hJLmayyZZbWL&index=8
As you know, you'll face three enemies at the same time. One is a caster, one is pure physical and the other is both. DO NOT kill one at a time as, once one of them is dead, the other two will become way stronger and have new moves. Drain their life equaly, so, once they get stronger, you'll be able to kill them quickly.
Do not stop moving during this fight. You'll be handling one of them constantly casting fire balls at you, other one always rushing in your direction and one that will stay mid range, for the most part.
Once they transform, the two melee enemies will have a new vertical attacks where their arms stretch, and those attack will go through walls, tombstones and whatever.
Once two of them is dead, the remaining shadow will be able to summon giant snakes that can do masive damage. So atack them if you can, to stop the summoning, if you can't, run and roll until the snakes are gone.
Keep calm, dodge and roll.