Laravel 5 Datatable Search not working in all columns of the datatable

Question

I am implementing datatables using three tables in my database. I joined all threeofthem together (employee, person, suffix). Datatable is reflected correctly. Butmy problem is when i search an employee using there first name or employee number,it isworkingfine and displays the employees base on what i search.However when i search using their last name, middle name or suffix, it says nomatching records even if that employee existed.

here is my bladefile

<div id="page-wrapper">
  <div class="row">
        <div class="page-header"><br>
          <h2>Personnel Information List</h2>
        <h5>Select Employee Personnel</h5>
        </div>
      <div class="row">
        <div class="col-md-12">
            <table id="EmployeeFilter" class="table table-striped table-hover">
                <thead>
                    <tr>
                        <th> {{ Lang::get("employee.employee_no") }}</th>
                        <th> {{ Lang::get("employee.employee_name") }}</th>
                        <th> {{ Lang::get("form.action") }}</th>
                    </tr>
                </thead>
                <tbody>
                </tbody>
            </table>
        </div>
      </div>
      </div>
    </div>
</div>


here is my script
<script type="text/javascript">
        var oTable;
        $(document).ready(function() {

            oTable = $('#EmployeeFilter').DataTable( {
                "sDom": "<'row'<'col-md-6'l><'col-md-6'f>r>t<'row'<'col-md-6'i><'col-md-6'p>>",
                "sPaginationType": "bootstrap",
                "bProcessing": true,
                "bServerSide": true,
                "bStateSave": true,
                "sAjaxSource": "{{ URL::to('employee_report/data')}}",
                "aoColumns": [
                      null, 
                      null,
                      null,
                  ],
                "fnDrawCallback": function ( oSettings ) {},
            });

        });

</script>

and here is my controller that returns the data table

public function data() { $personnel_employee_list = Employee::join('person','employee.person_id','=','person.id') ->leftJoin('suffix','person.suffix_id','=','suffix.id') ->select(array('employee.id','employee.employee_no','person.first_name', 'person.middle_name','person.last_name','suffix.suffix_name')) ->orderBy('employee.employee_no', 'ASC');

    return Datatables::of($personnel_employee_list)
        ->add_column('actions', '<a href="{{{ URL::to("employee_report/personal_info_sheet/" .$id) }}}" class="btn btn-info btn-sm"><span class="glyphicon glyphicon-list-alt"></span> View Details</a>
                  <input type="hidden" name="row" value="{{$id}}" id="row">')
        ->editColumn('first_name','{{ ucwords(strtolower($first_name." ".$middle_name." ".$last_name." ".$suffix_name)) }}')
        ->editColumn('first_name','{{ ucwords((str_replace("ñ","&#241;",str_replace("Ñ","&#209;",$first_name))." ".str_replace("ñ","&#241;",str_replace("Ñ","&#209;",$middle_name))." ".str_replace("ñ","&#241;",str_replace("Ñ","&#209;",$last_name)) . " ".str_replace("ñ","&#241;",str_replace("Ñ","&#209;",$suffix_name)) )) }}')
        ->removeColumn('id', 'middle_name', 'last_name', 'suffix_name')
        ->make();

}

my data table