You had mentioned in the Post that you had only son who was the sole breadwinner of the family. If that is true and you were fully dependent on him, you can make an appeal to the PF Authority thru the employer of your son and if they don't agree approach directly to the PF Office (Meet PRO or The Asst. PF Comm. of his group) with your son's PF A/c. details. Inform them that you were fully dependent on your deceased son and also nominee to PF.
Although his wife claims as a legal heir for insurance money, You may state in your application that your daughter in law may get remarry after getting the insurance claim. If your DIL is a working woman, you may state that she has source of income.Your case may be considered on humanitarian ground for some percentage by the PF dept.
You may quote the following for Deposit Linked Insurance Benefit.
Who can claim the benefit in EDLI or Employee Deposit Linked Insurance?
This insurance exactly works like term insurance. Hence, after employee death, his nominee can claim the amount and below are a few points to consider.
A nominee can claim the amount.
In case there is no nomination, then the legal heir can claim the amount.
If the nominee or legal heir is minor, then a guardian of minor nominee can claim the amount.
Best of Luck,
From India, Thane