At first, ascertain the terms and conditions of their service as would have been mentioned in their letters of appointment. Is there a distinct clause for termination of employment by either party giving one month's notice or salary in lieu thereof? Is there any other clause that has a different application for a certain class of employees - such as Trainees or Probationers?
Did the Company issue any letter to the employees while relieving them? Did the employees have to submit letter of resignation to the Company? In case, they have been asked to submit letters of resignation, did they specifically say that it is a notice for resignation? Technically, if they have submitted resignation and not provided for notice, it will appear that it was the choice of the employee to leave and notice period has been waived by the Company.
Look into all the above facts and if there is a case, then get each of your friends to write a letter to the Company claiming the notice period pay.