The legal heirs of your father i.e., you, your sister and your mother are entitled to an equal share in all the assets left behind by your deceased father.
It is not known that whether your father's deposits was acquired by your mother on her own or by a Will bequeathing the same in yor mother's favor.
However being a nominee of your mother's deposits will not entitle you to take the entire deposit amount by yourself.
The nominee is just a trustee to receive the money on behalf of the legal heirs and the nominee should distribute the same to all the legal heirs equally.
In the absence of yor sister, her own legal heirs namely her husband and children shall be entitled to her share in the deposits and other estates.
In the event of your own death and being unmarried at the time of death your properties shall devolve on your class I legal heirs, and in the absence it may devolve on class II legal heirs.
Your sister being one of the class II legal heirs, upon her death her own legal heirs shall be entitled to inherit your properties.