I know....the full game will fix that to make the hints more obvious, I've received similar complains. Anyway!
1st rose: Next to the Angel Statue
2nd rose: On the library, use Amarant to break crate.
3rd rose: Do the soldier puzzle and paint it red with the fountain.
4rd rose: After getting 3 roses, check the library portrait. There's an open book now. Use the shovel from the storage.