Bharati,
Use GUI_UPLOAD function module to load flat file to a local table, use function module BAPI_BUPR_RELATIONSHIP_CREATE to create the relationships. You have to write a report using the above function module to create as many relationships as you would require.
Also do not forget to use the function module 'BAPI_TRANSACTION_COMMIT' to commit the work to DB. Hope this helps.
Same solution as Sudheer mentioned above.
Pavan.