The money in the account of the person deceased is handed over to the nominee. If your mother had named anyone as a nominee he/she is entitled to get the money. Legal heirs have a claim to the money. Nominee is just a trustee. Therefore you have to share money in her account with your siblings.

I presume your mother died intestate 

on mother demise you and your siblings would be legal heirs 

bank would insist on succession certificate before they permit you to access the funds lying in said accounts 

contact a local lawyer for  applying for succession certificate 

Well, legally your siblings have an equal share in any movable/immovable assets that belonged to your mother. If it was a joint account then you may operate the account.

You need to share money with your siblings 

if they submit their NOC bank would permit you to access the funds lying in said account 

- As per the RBI , in case of death of one of the joint account holders, the survivor will hold the money only as a trustee of the legal heirs unless she herself is the legal heir

- Since, the said account is in the joint name of you and mother , it means both having equal right over the fund . 

- Further, after demise of your mother , her half share of the fund can be claimed by the all legal heirs equally including you. 

- Hence , there may be requirement for Succession Certificate to get the entire money from the bank , however some banks only needed NOC from other legal heirs. 

Sharing of money left by mother is matter of agreement  among legal heirs. But bank will insist on succession certificate  from local Court. An application for such certificate can be filed in district Court by any one of legal heirs residing in India. You can appear in succession proceedings from abroad through GPA drafted there taking attestation of notary or Indian consulate and withdraw you agreed share from SBI branch in foreign country. You can also get the  deposits transferred to by Local Scheduled Banks on the  basis of succession certificate  issued by Court.

If you are either of survivor in that bank account then you  can other wise you need to approach court seeking orders of withdrawal after her death

Even though this is a joint account, your siblings may lay their claim for a share out of your deceased mother's money parked in that account.

Though, you can legally transfer the entire amount to your account  held with another bank without the permission or consent of other siblings, it would always be advisable that you share your mother's money with them proportionately to avoid litigation that may arise in future in this regard.

However the bank may not insist on any formality since you are one of the joint account holders. 

Your mother has been survived by her legal heirs who are entitled to a share out of her movable and immovable assets, hence it is always advisable to share the amount with them to avoid any litigation in future. 

1. What was the mandate given in the said bank accounts for  operation of the same? Are they former or survivor or anyone?

2. In any case, you can transfer the balance amount to your bank account first and then close the said accounts.

3. If your siblings can prove that the amounts kept in those accounts are deposited by your father from his earnings, then other legal heirs of your father can claim share of the same. 

4. To avoid this you shall have to prove that those amounts have been deposited from your earnings or from the amount gifted to you by your deceased father. For gifting immovable properties like money, no gift deed is required to be registered.

1. You shall have to share the amounts with the other legal heirs of your deceased father on grounds already explained in my earlier post.

2. In that case, your other siblings also shall have to share with you the amounts kept by your deceased father in the joint accounts with them on the same ground.