1. Since your mother was the 2 Nd Wife(when the first wife is alive), your mother does not get any share in your deceased Father's property.
2. The first Wife and her 2 Children, you and your Sister are entitled to equal share in the property left behind by your deceased father. In other words, each legal heir is entitled to 1/5th or 20% share in the property left behind by your deceased father.
3. You and your Sister (2 Children from your father's 2nd wife) are entitled to equal share and on par with your father's 1st Wife and her 2 children in the ratio of 20% each.
4. In case, if the issue cannot be settled through talks, then file a case in Civil Court for Declaration, Partition and separate possession of the property by metes and bounds.
5. Nobody can say and claim that your mother's property in her name was financed by your deceased father, since your mother was also a Government servant and had put in sufficient service which enabled her to buy the property.