1. Strictly speaking your father is the absolute owner of the flat and also the amount lying in the Bank in the joint account of himself and your deceased mother,
2. Your mother had, during her life time, had deposited all her retiral benefits in the said account probably with the withdrawal instruction allowing either or survivor,
3. Based on the above instruction, your father is the absolute owner of the said amount,
4. had he not been so authorised, the Bank would not have allowed him to deal with the said amount,
5. You can lay your claim for your share of the amount releases by the employer of your mother after her demise, if any.