Short walkthrough on parts people are commonly stuck :
1. If you have the hammer and confused what to do next, try checking on right most room on 2nd floor. the bottom right room will have an interactable cupboard (provided you lit up that part of the room, else it wont appear) which have the code for safe vault. You can figure out what to do after that.
2. After you help the mansion owner, you also get the 1st floor storage room key, where you'll find the lesser talisman to defeat the tentacles guarding the box at 2nd floor (important for good ending).
3. To continue, you just simply need to walk around back and forth until Mansion owner goes back to the treasure room, just go between the safe area and front area repeatedly until he goes to the corridor, and then back to treasure room. This will trigger an event and he'll give you the key for the treasure chest. After that its straightforward
Enjoy the Game!