This isn't a really hard battle, especially if you're a melee fighter that can use AoE attacks. The main magus, the two priests and the hollows can be easily taken out with powerful melees. Just be careful of the crawling undead as they might be hard to hit. Take out the priests first since they can use beam attacks. You can use the benches to fall back give yourself distance from the enemies in case you need to heal. Overall, this shouldn't be a hard battle.
This guy is impossible, what are you talking about?