You can get the good ending by helping 3 people at least (and not qualifying for the other endings with higher priority, like killing a lot of animals or killing more than 1 person).
To help the warlock (devil guy), you have to go to the forest and let a dark butterfly follow you all the way to his lair. If you have not spoken to him at all, the butterfly won't appear in his lair, but you can go back one screen and it will reappear again. So speak to him, then bring him the butterfly. That way he will summon the Dark Fire and you will complete that quest.
To help the huntress, you can either cure or kill the Fire Snail. The only way to kill the fire snail is with the Dark Fire, so to kill the Fire Snail you also have to help the Warlock. On the other hand, there is a secret place in the game that will spawn a Healing Cucumber after you've spoken to the Huntress (provided she is still alive). So if you find that place and take the cucumber, you can go to the fire snail and heal it instead. Both solutions will resolve the quest.
Thank you for your kind words :D