Relinquishment deed for a mortgaged property.

We have taken SME loan from a bank for our pvt ltd company and one of few collateral securities includes one immovable property in the name of relative of the directors. This property is jointly owned by a Mother (Aged 90 plus) and his son (Aged 60 plus). Recently son has expired unfortunately. He did not write his will and as per succession rules his share has devolved to the following family members, deceased's one son, two daughters, deceased's wife and deceased's mother (90 years plus as mentioned above). Now all these members old aged mother, two daughters, deceased's wife want to do haq tyag (relinquishment deed) in favour of deceased's son. So he will be single owner. Now the questions arises as follows:- 1. Sub Registrar has denied to register relinquishment deed without seeing the original registry of the concerned property. Original registry is kept in the custody of the bank as aforesaid. Whether registrar is legally right in saying so. There is a huge difference of opinion on this. 2. Whether such relinquishment will attract stamp duty which is already paid on the mortgage of the property to the bank. (Here I am not asking stamp duty on relinquishment deed, I am asking stamp duty on Equitable Mortgage, please note that there is no enhancement in loan amount). 3. Bank is saying that relinquishment can not happen of a mortgaged property and first it will have to release the property by taking approval from competent authority and then re mortgage of the relinquished property with new owner will take place, but this will attract heavy stamp duty to us. Stamp Duty in MP on EQM is max. Rs. 10 Lacs which will get attracted in this case. Can this be not done after taking NOC from the bank instead of releasing the property from mortgage. 4. If we give NOC of the bank to the sub-registrar for relinquishment then also he may insist for show of original registery and deny to register haq tyag. Idea is only to save heavy stamp duty and get the work done.