Married daughter Right over fathers property

Respected Sir, We are a joint family of 4 brothers and 3 Sisters.My father died before marriage of my sisters. I along with my brothers borne the expenses of their marriages and have settled them with fair share of immovable properties and some liquid assets like jewellery and cash.After all their shares, we 4 brothers and my mother(widow) are left with only one house(self acquired by my father).My mother used to stay in this house and recently my mother died without any will.So all my three brothers being in different parts of world wanted to sell the house.As i am staying in India I wanted to buy the house from my three brothers.But problem arose when one of my sister started claiming equal right(1/7th) in the house.But other two sisters agreed to sign as witness(though they demanded some cash which I agreed). the sale deed is executed without that sister's consent and its also been 1 year since this is done ....My sister has not filed any case but often threatens me to settle her with cash else she would file a case. Given the fact that she has been given fair share, a)Are her claims legally valid according to indian law? b)what should be my legal stand if she files a case? c) whats your personal opinion to settle such matters?