I think this should do what you want.

        select
          p.inst_id    coord_instance,
          p.indx       coord_pid,
          s.inst_id    slave_instance,
          s.kxfpdpnum  slave_pid
        from
          x$kxfpdp  s,
          x$ksupr  p
        where
          s.kxfpdpnum != 999 and
          p.addr = s.kxfpdpcpr and
          p.inst_id = s.kxfpdpcin
        order by
          1, 2, 3, 4
        /

Is there a way to associate parallel query processes with the session that's running the query?