The will states all assets to be divided equally between two siblings but one had a joint account with the deceased.
The answer to your question depends on the type of "joint" savings account. If it was a joint tenants "with rights of survivorship" savings account, then the surviving joint owner (sibling) has automatic rights of ownership over the whole account at death, and the account does not pass according to the Will. Typically, in this situation, the bank will simply require a death certificate to remove the decedent's name from the account, and the sibling would then own the entire account. If the account was not designated as having "rights of survivorship," then the decedent's share of the account would pass according to the provisions of the Will. However, this response is based on limited facts...various factors may require a different response.