Check out Import Records and its many options. This is the tool you should use to move data from your excel files into tables in your filemaker database. It can also be used to copy data from one filemaker table to another.
To import data into 4 different tables, you'd import records four times--once for each target table in filemaker. You'll need to analyze your data to see if the excel data has the correct values to support relational links between your four tables. If you have a column in the spreadsheet that unqiuely identifies each row, you have a start on that--though the details depend on how you need to structure your data and what form the data takes in the spreadsheets.
Whenever you try out an import records operation, make a back up copy of your file first so that you can toss the file and try again if you don't get the results you expected.