I don't know is someone is still interested by it, but i managed to conclude both quests :

  • i didn't give the blood stone to Frederick, he just stand up and left.
  • the imp was in Maradino's lair and i told him to stay hidden, then i gave him the potion of bravery. He left to the place Frederick was. And when he saw the blood, he thought that his former master was dead, so he just left free.