Ghoul Duke- After you go through the caves and kill all 4 necromages, the ghoul duke will spawn in front of the door. He is rather easy to kill and has no special attacks. Just tank and spank. A knight tanks, healers heal, and dps attacks.
Flowing Chaos- This boss is on the right after you walk into the first chamber. There will be a door and another room leading to where he is. He looks like a giant green ooze. He doesn't have much special attacks, but he casts poisons on people and has a poison AOE. Occasionally, he also casts fear on the tank. Still, he's pretty easy.
Cruel Eater- This guy is just like the ghoul duke, but he is stronger and has an AOE called "formation breaker". It can be interrupted with silence, surprise attack, charge, throat attack, etc. If you can't interrupt it, just move away a bit. It has a short range. Other than that, he is simple.
Hollow Shell- This guy resembles a huge necromage. He casts fireballs a lot at the tank and can also cast silence (i think). He has an AOE "Release darkness" which has a decent range and is like a few explosions one after the other. This takes about 5 seconds for him to cast and can be easily interrupted, but keep in mind that it actually takes effect before the spell bar is totally full. Your best bet is to interrupt it as the range is large enough to get people even decently far away. But his most annoying quirk is that he summons zombies to attack you. This is what really kills most parties, as we all know that lvl 25s aren't good at killing zombies. I suggest that you have 2 healers- one to heal the knight and one to group heal. The knight should do whirlwind shield as soon as they spawn to draw their attention. For the others, just try to stay alive and protect the healers.
Ancalon- the big lady herself. She is a difficult boss to fight, far stronger than the others. She fights like Shell, but is more aggressive. She will occasionally chain people in place to keep them from running away. She has silence, release darkness, and spawns zombies and shadows. Kill them as quickly as possible. She can heal herself, so watch for any irregular spells and try to interrupt as many as possible. She also has an interesting spell that is incredibly annoying to higher levels. She can "flick" them out of her room and out of combat. I'm not sure if she does this to lower level tanks, but I am very often flicked as a level 53 scout when Im running people through.
Hope that helps.