Since the property has been offered as collateral security and has been mortgaged in favor of bank,  you may have to wait until the entire loan amount is discharged after which your mother can execute a registered settlement deed in your favor. 

You'll have to seek for a NOC from the bank to transfer the property in your name.

Only after loan is repaid can your mother execute registered gift deed in your name 

2) bank will not permit any transfer till loan is repaid 

1. Let your mother execute a Gift Deed in your favour registered in the jurisdictional Sub Registrar's Office, inspite of property registry is with bank.

2.  Alternatively, let your mother execute a WILL, for the property, in your favour, so that your brother can't claim it for which you are only paying the EMI and the brother is not paying.

Mother should execute registered gift deed in your favour during her lifetime after repayment of loan 

If the documentation of Gift Deed or/and execution of WILL by your mother in your favour, is correctly and legally drafted, without ambiguity, then it will be cent percent secure and after your mother's death, even if your brother claims/challenges it, it would be futile for his effort.

Execute a triparted registered agreement with bank & mother on the one side and you on the other. Get the loan transferred in you name as principal borrower. Close the loan, cancel the MODT, collect originals from bank. You title cannot questioned, you are absolute owner of property.  

You can make Gift deed or WILL and registered that with concern SRO office of your flat area.

I suggest to you kindly make Gift deed which irrevocable in the future.

She cannot transfer the property as gift during the subsistence of mortgage loan. She can write a Will but it will be enforceable only after her lifetime. 

She can even cancel that during her lifetime without informing you. 

She can execute a gift deed by transferring ger share in your name without documents of bank

- Since, the property is mortgaged with the bank , then washout completing the full amount of loan , your mother cannot transfer the said property in your name legally. 

- Further, if the said loan is in the name of your mother , then you can take NOC from the bank after executing an agreement with the bank to transfer the loan amount payment in your name. 

- Further, your mother even during the loan period can transfer the said property in your name after executing a sale deed or gift deed , hence discuss with the bank to transfer the said loan in your name and to give permission to execute a gift deed. 

Dear client I am sorry to hear that but in this case you can change the nominee name in the property or your mother can make a will in your name

Respected Sir,

You may get transferred ownership of the property in your name through transferred deed. No stamp duty is to be paid on transfer deed within blood relation.

She can still execute a will qua the property. Gift deed would also require NOC