The experts have explained.
The female is not legally wedded to your father and her son is not sired by your father and seemingly has not been adopted by your father by a valid deed.
If your father has died but has not left any WILL in favor of the female and her son Or has not transferred the property in their name by a valid and legal and registered deed then you have a claim being ClassI legal heirs of your father.
You may pursue the pension rules of the establishment that is disbursing pension.
The family for nomination and disbursement of pension is clearly defined in the pension rules.
It is surprising how the female is getting pension.
Find out from the office that has processed the pension claim or that is disbursing pension OR even if you have to pursue thru RTI.