Issue legal notice to sister in law to vacate your house 

2) if she refuses file suit for eviction 

3) kindly clarify whether your father left any will or died intestate .if he died intestate then brother has 33 per cent share in one plot .since one house has been built on 2 plots you cannot force your sister in law to vacate on brother demise 

4) 

Section-2(e) of the Act defines land grabbing as an activity performed by the land grabbers as an attempt to occupy any land with or without the use of force, threat, intimidation and deceit, over which they don’t have ownership, title, or physical possession

Actions in violation of these provisions shall invite imprisonment for not less than ten years. This period of punishment may extend up to fourteen years.   

5) provisions of land grabbing act would not be applicable to sister in law if your father died intestate 

You have rights in only one plot though the plot was built combining two plots. 

Now you and your father have to initiate action jointly to eject her out of the property. 

She has not grabbed your property. 

She had been residing in that house along  with her husband. 

Now after his death she continues to live there, hence no criminal offense done by her. 

You have to file a suit for ejectment along with your father to throw her out. 

1. House constructed on land purchased by father and son. If the father is no more, the property in hands of son becomes ancestral property in which legal heir of deceased brother will be entitled to the share deceased ancestor.
2. If deceased brother has contributed any funds—however little—the house in the hands of father and another son will become ancestral property.
3. Widow of brother can claim the share of deceased husband in the house.
4. She an also claim right to shelter in the house under Protection of Women From Domestic Violence Act, 2005.
5. It is not possible to throw her out of house.

Dear client I am sorry to hear that but in this case you can only claim the ownership of the house that is build on your property and not on your father's property because the father's property belongs to all his legal heir. Atmost you can ask for compensation for the property or house that you have built

Respected Sir, 

Your brother's wife has right to receive share in the property of his property.

- Since, the said property is jointly in name of you and father , the the wife of your deceased brother cannot continue to live without getting your consent . 

- Her position in the said property is like a licensee via your brother, and nothing more. 

- Hence, you can terminate the license after sending a legal notice to her , and if not vacated then file a Mandatory Injunction suit before the court for evicting her from the premises. 

You need to file eviction proceedings against her. If the flat belongs to senior citizens then you can also apply under senior citizens law