Event 41 is located in the same place where you spoke to Chemica in the bewitching flower garden, where you defeated the mutated tentacle. At the bottom is a boss, you might have to employ a strategy with your tank focusing on just guarding. Since i see that you've completed the quest in defeating the grim reaper, you've unlocked the class that the succubus can teach you. Try learning incite(or taunt,that skill that causes all enemies to focus your tank for 5 turns) from the nightmare class,and just keep your tank guarding while your healer focuses on party heals, and you should use a mage class with fire magic,since the boss is weak to fire. The reason why you want your tank guarding is because when the boss bites deep,it's normally a 1-hit KO (since the damage it deals is equal to your max health) - this can be countered since guard will reduce it by 50%(or more if you have certain skills in the warrior tree), allowing your tank to survive. It's been a while, but i think the boss uses a lot of sleep, so you might need a sleep guard amulet to manage that.
Alternatively, for damage, if you have the flamesea wyrm accessory(obtained from the Guardian in the lava area a few chapters back), equipping that on a physical damage dealer enchants their attacks with fire, also an option to do a lot of damage.
Event 30 can be found in the ancient wolf's tree - located east of central haven (you might have to go west from Harsh outcrops,located from the Miruess army HQ) - you climb to the top,talking to one npc along the way and defeat a sparkling butterfly, then go back to her and she'll return back to the training grounds,giving you access to the valkyrie class. As for the boss, you might need to level up a bit (It's a bit tougher than most things you find in chapter 4 for now.)
I think the boss uses a 1-hit ko move every few turns, so you'll have to get your tank to use taunt, and then revive her, i think theres no way around that.