For your deduction table:
$crud->set_relation('employeeID','employee','employeeID');
This should go into your deductions controller you will receive a dropdown that displays employeeID and the objects those ids belong to.
For your employee table
$crud->set_relation('employeeID','member',memberID);
This should go into employee controller you will receive a dropdown that displays employeeID and the objects those ids belong to.
Hope this helps.