Will of my mother

I am the eldest of two children of my mother and father. The other is my younger sister . I had love married a girl from a different caste but living with her a very satisfying married life. We are both 50 yrs. We have two children a daughter and a son. Since our caste demands a lot of dowry from the bride and since I don't get it for my marriage , my mother is very jealous of my wife. More over since my sister's arranged marriage ended in divorce and later had a second marriage but living happily in Canada , my mother has lot of sympathy on my sister. Me and my wife are currently taking care of my mother. Father expired of Alzheimer's disease in May 2015. All thro my mother had over ruled my dad. She is very arrogant and does not enjoy a good relationship with any relatives and neighbours. With great difficulty we are bearing her and taking care of her. She has harresed my wife endlessly and the whole neighbourhood is witness to that. Now she has willed her property and looks like she has given me only 25 % of her assets. 75% seems to have been given to her daughter who lives in Canada. I have seen her will confirming this. I am financially OK but feel cheated by my mother. She is being unnecessarily motivated by my sister to evict me from the house that my father and mother together earned. Unfortunately the property is entirely on my mother's name. I was the one who built the 2nd floor and used to collect the rent myself. But now she wants to evict me from her house and give the entire house to my sister including the portion I built.( 2nd floor). I have no documents to prove that I constructed the house. Except for the contractor who will come as witness for the same. All my father's bank accounts were made into joint accounts when he got Alzheimer's disease. This is a very raw deal and I would like to contest this will of mother. Further I want to teach my sister a lesson as well. She and me has never had cordial relationship as my mother practised the " device and rule policy" . as such I have little or no concern for my mother or her daughter. I and my wife was with my father during the terminal days of his Alzheimer's disease. Now me and my wife feel we have been used and then being thrown away. Can I file a dowry harresm3nt case against my mother and sister to put them behind bars. I have concrete evidence for the same. I can also ensure that my sister will never be able to come to India ? Further what other legal options do I have ? Kindly advice.