family matters

Our family was consisting of Father, mother and three married brothers. We are having the agriculture land which is earned by my grandfather . My younger brother was not qualified and hence we both brother have supported him financially till marriage My father is retired and has no pension. My father mother was also dependent on us(particularly we 2 brothers). After marriage of my younger brother my mother encouraged his wife to complete the B.ed and she got service as teacher in reputed school since last 3 years. My father has built-up a house from his earned money(After retirement) but the property was taken on the name of My mother .Hence She had the non-movable bungalow property on her name. My Mother passed away in 2012 year without making WILL. Now the heirs are my father and we 3 brothers as we do not have sister. I like to know whether these are legal heirs? Unfortunately my younger brother also passed away last week. Now his widow having age of approximately 36 years. As the age is less we are planning encourage her for second marriage and take a lead if she gives consent for same. I like to know who will legal heirs if she marries with other person and who will be legal heirs is she opt not to marry. As Further my father wants to make will that the agricultural land shall be made in the name of we brothers only as we only supported him after retirement ? Is it legal?