1. You can load the two tables from SQL database, but you need to find out how to link the tables properly. Based on your explanation, the first table is defined by Year and Customer, and the second table only has Customer. Don't you have Year in the second table? Correct linking of the tables is th key to correct reporting/analysis in QlikView. Perhaps you could look up some available training on QlikView scripting. Those issues are covered there.
2. The "sub-sheet" is implemented in an object called "Container". You can list several objects (charts and tables) in a Container, and their names will be presented in tabs.