You can find out which files are linked via this command

DSPDBR FILE(LIBRARY/FILE_NAME)

And in spool file you can find results

Files Dependent On Specified File                                     
  Dependent File         Library       Dependency   JREF    Constraint
      FILE_1             LIBRARY1      Data            1              
      FILE_2             LIBRARY2      Data            1              

Then you can try first to delete member with same name in joined logical files