Importing data of same company

Hi professional freinds.

The job of book keeping is divided between 2 people, one looks after Sales and Receipts and the other all the rest.

Tally.ERP 9 is used by both of them and the objective is to merge both the data.

We have exported the Daybooks and imported them in the data of Sales guy  but it doubles the amount of all the ledgers, without ignoring the duplicates.

How can the objective be acheived? Kindly help.