More information about the table relationships and the reason for redudant data would be helpful.
Is the redundant data in columns of differnt tables or do you have duplicate rows?
Does the data need to be stored into another table or could you create a view?
If the tables have a one to one releationship, you could create a view that joins each table and returns just the columns from each table that you want.
Randym is right. Perhaps a good way to figure out how the rows match up is to create samples in Excel and have the data approved by your customer. Then you can write the SQL based on how the data lines up in Excel.