Shizuku's family used to have more money.They lived in a house, and Shizuku's father was a salaryman. When Japan's economy started to slow in 1990-1991, he lost his job and took a lower-paying job at the library to make ends meet. The family lost their house, and moved to the apartment. Shizuku's mother went back to get her master's degree to hopefully regain some of the family's lost income. Both daughters reacted to the change in opposite ways: Shizuku's sister was more of a realist, resigned herself to a fate of working part-time jobs, and saved up enough money to move out. Shizuku, who would have only been about 10 when the economic bubble burst and therefore less knowledgeable about what was going on, resorted to reading fictional books as a (subconscious) form of escapism.
Louise was Jewish. She died in the holocaust.
The grandfather clock was found in Castle Cagliostro.It's a beautiful, intricate design, so is probably worth a lot of money and tells the story of two lovers destined to be apart (not wholly dissimilar to how Lupin and Clarisse ended up).