Enquiry and holding of Gratuity after on roll death of employee

My father was Scale-I employee / branch manager in Punjab National Bank. On the day of his death his branch was under audit. In the afternoon he visited his Regional Office from his branch office to submit some report. Our residence was also in the same city in which Regional Office is situated. He died in the evening due to heart attack. During his life time no enquiry was initiated against him. After his death rumors spread that there was some financial irregularities in the branch and my father was blamed for the same. Punjab National Bank took almost a year to release my mother's pension. Pension amount was reduced to 1/3rd of actual pension i.e. only family pension was released whereas full pension for 08 years should be released. Gratuity amount was also withheld. We also got to know from different people that CBI enquiry was ordered. We waited patiently for years for CBI or Bank to approach us for any enquiry. They never approached us. After few years we obtained these information through RTI. We also repaid the pending Housing Loan taken by my father through some of the Fixed deposits that my family had in the same bank. Source of the Fixed deposits can be traced as almost all fixed deposit were made through Rec ruing deposits. Bank also seized the portion of Fixed deposit that left after winding off of housing loan that too without taking any permission. So far whatever we know in this case is through the RTI only. Bank or CBI has never approached us regarding any enquiry. My query is that the actions taken by the bank is legally tenable or not. Shall Bank release the Gratuity amount and revise the Pension.