Thank you everyone for your suggestions and insight. After rethinking our plans, we've decided to make the Buckingham Palace tour through the Royal Collection Trust our priority. The tour was not available in our last visit 15 years ago. We'd like to do the Royal Day Out tour, but tickets aren't available for September yet. However, we can purchase standard admission tickets to see the State Rooms. Does anyone know when the Royal Day Out tickets might be available? I wonder if we should purchase the standard admission tickets so we don't lose out. I assume it's a tour in demand. We've scaled back our initial plans and though we'd like to see the Tower of London and its Crown Jewels, alot depends on the Buckingham Palace tour.
We are staying two nights in London. I'd like a longer stay, but my sister has limited vacation time.