who will be the successor and what is procedure to introduce a will ?

dear sir, my name is nihal ranjan, i am hindu by religion , the head of my family was my grand father(late s.k singh) who died in 2007, he was the owner and sole proprietor of the house, he purchased a land in ranchi,jharkhand and build a house , he had 2 sons and 2 daughter,the daughters are at present married and are seetled with their husband.. .The eldest son (late sanjeev) was married to a woman (rita)and they together had a son(vikas) , after the birth of the son(vikas) three year later he (late sanjeev) died in a road accident. The widowed wife(rita) of (late sanjeev) got married to the yonger son(rajeev) of my grandfather who is my father. myself(nihal) is the only son of rajeev and rita....lastly at present the members in my house are - my grandmother, my father , my mother , my brother who is the son from my mother and my late uncle(late sanjeev).....my grand father died without making any will then now who is the successor and who will enjoy the full ownership.