Hi,
Your option is to file a summary suit for claims which is due to your father with interest. This includes gratuity, pension benefits and other retirement allowances.
Regarding the P.F, the company has to verify the application and send the P.F application to the P.F office concerned and the payment is done without any delay.
First send a legal notice to the company as a legal heir of your father , claim the above mentioned benefits dues with interest, in case the company is not responding things rightly, move to a civil court.
Discuss this matter with a an advocate who handles civil cases in your area and proceed.
Human Rights commissioner does not have jurisdiction to entertain this matter.
A writ in the high court is not necessary as the first legal forum is civil court in your area.