Grunkle Norbert's Great Lost Fortune

Across from the door is a locked cabinet.

Pick up the second-to-back record from the record box ("The Barber of Seville: Act IV Overture") and play it on the record player. The glass cabinet will smash when the opera singer sings her high note. Grab the hammer and head back to the hall to smash the vase for your second note with a key on the back.

Mr Frederick and Ms Humphreys want one spot in particular.

Follow the party planning notes to satisfy all the guests' needs.

Clockwise from the far left of the table as you enter:
Mr Frederick -> Mrs Baker -> Mr Baker -> Mr Stewart -> Ms Humphreys -> Dr Wilson

Check the room on the left. Have I seen something here before?

Head into the room on the left where you see a map on the wall. On the desk is a book describing several artefacts. Pick up the book and flick through to find artefacts you've seen throughout the house. Spoiler: the artefacts you will find in the house are the tiki totem (Indonesia), the horn (The Netherlands), the elephant (China) and the vase you smashed (South Africa). Pinpoint these locations on the map with the pushpins on the desk, in an X shape. The crossing point reveals the solution. Go back to the library and interact with the bust statue to activate a secret lever revealing the vault. Inspect the book about the country at the crossing point (India) and look at the back for the 4-digit code (4026). Type in the code to open the vault.