Harassment of a lady Senior Citizen by her son & daughter-in-law

Dear experts, I am asking the question / seeking solution on behalf of my Mother. She is a widow who is 65yrs of age. We have two properties. One is shop which is in name of my mother & my late father jointly. Secondly we have a house which is in name of my late father. My brother got married on July 2013. Since then his wife has been threatening me and my mother that she will file a false dowry case against us if her demands are not met. She wants that we should give shop to my brother so that they can sell it and secondly we should give half of the flat to them. They wants that we should divide the flat by erecting a brick wall in the flat. Since my fathers death both my brother & elder sister has not taken care of my mother. They frequently quarrel with us and use abusive language. What should we do in this case as we dont want to sell our flat? Kindly guide me if my mother can restrain them from entering out home as my brother & his wife are not living with us since Nov. 2015.?