While you might have be thinking what happens in case the FD holder dies and there is also a joint owner to the account. If the depositor happens to be a Hindu then the estate succession will follow the principle of the Hindu Succession Act 1956. And anything in the name of the deceased will then be distributed to legal heirs.
Also, in the case when the joint holder or survivor is there for the account, unless specified and made cleared by the depositor, that he wishes to transfer the proceeds or gift the instrument to the joint holder, the proceeds are transferred to him or her (joint holder, but he or she is merely a trustee of the funds.
And the survivor or joint holder of the account is held responsible to transfer the funds to the heir in accordance with the succession law.
The case holds true when there is a nominee to the account, the nominee is also the trustee who as per the succession law need to transfer the proceeds to the heirs of the deceased.
Therefore, with regards to the fixed deposits, it shall be subject to the same principles applicable to interstate succession of a Hindu under the Act and each of you, including your mother, sister and brother shall be entitled to a one-fourth share in the fixed deposits.