Both files should have Table Occurrences (The boxes with table names found in Manage | Database | Relationships ), that point to the same data source tables in DS.
On DE, add a table occurrence to your relationships graph using the button on the far bottom left. Use the add Filemaker data source option to find and open DS. Select the correct table from DS as the data source table for this occurrence. Repeat for every table in DS that you need to access this way from DE. Link these in relationships just as though the tables were defined on the tables tab of DE.
Now you can set up layouts in DE that refer to these Table Occurrences in the "Show Records From" box of Layout setup... and can enter data into them just as though the table were defined in DE instead of DS.
If you are interested in learning more about table occurrences and how they can be used: Table vs. Table Occurrence (Tutorial)
Thank you for your response - your advice worked great!!!
Sorry for taking so long to reply, I have been traveling and just now tried your suggestion.