DEAR HARRIETTE: My 23-year-old brother has asked me for a substantial loan to start a new business. While I want to help, I’m feeling uneasy about lending such a large sum. At 47, I’m more cautious about my financial decisions, and this request feels quite big. I’ve seen how starting a new venture can be unpredictable, and I’m worried that a possible financial setback could affect our bond if the …