does every sheet in the excel workbook have the same layout of 4 columns with the same names? I ask because this looks like a great opportunity to use the Tableau Union feature with the workbook. You could then use the sheet name as a filter to view 20 different sheets of data within a single view.
Your example data is duplicate data in Table 1 and Table 2 so you can't clearly see the difference in the attached Tableau 10.3 workbook but this is a quick example of one solution if union join is possible.
I hope that helps.