1. If the property were to be your father's self-acquired property and had gifted this property to your sister by executing a gift deed in the Sub-Registrar's Office, then it is in order. However the execution of gift deed can be challenged in a court if the execution of gift deed was due to fraud, coercion, threat, etc.
2. Regarding the balance in your father's bank account, he would have nominated a person/persons and nominee is only a custodian of the proceeds on behalf of other legal heirs.
3. Regarding other items such as Gold, Bonds, etc.,Whether your father had executed a 'WILL'?. If he had executed 'WILL', then the share/s would devolve to the beneficiaries as per the contents of the 'WILL' and in the absence of 'WILL' i.e., if he has died intestate, then the share would devolve equally to all the legal heirs, i.e., your mother, you and your siblings. A succession certificate can be obtained by all the legal heirs from the court.
4. It is really unfortunate to know that your father was not allowed to meet his own family members minutes before his death.