Division of property among brothers

This is regarding a joint property in the name of my father. He is passed away almost 12 years back after which i demolished the 2 small single rooms on area of 87 sq yards which belonged to him. My two brothers were staying separate and i was staying with my mother who is mentally ill. So, after he passed away with the pension money that my mother received, i demolished old structure and constructed 3 equal portions (2 small rooms each including kitchen) and a common washroom for the 3 portions.Then money was not enough to complete construction so i took some loan of around 80k to 1 lac and completed 2 portions ( 1 for myself & 1 to give on rent, so that me & my mother can survive as i was only 20 years old and was youngest son). My two elder brothers never take care of my mother and they are married with 2 children. Then the elder brother came in and completed the one porion (plastering,paiting,electrical work) and stayed there and is still staying there. One portion was on rent and in another i stayed with my mom until i got married. I got married 6 years back and then i stayed with my wife and the other portion which was on rent was vacated so that my mother can stay. 4 years back second brother came and claimed his right as he was ill and could no go for work. So my mother gave away her portion to him and he promised to pay the construction money which i had put on my own. It was written on stamp paper but he never paid. My wife had delivered a baby & hence we moved out for rent and i gave my portion to my mother so that she can stay. Now the elder btother constructed first floor with our permission, but we said him not to construction entire floor but to leave one portion above. But they constructed entire floor and itr is still in construction. He is denying of giving the one portion in ground floor to us. We siad we will combine 2 portions in G floor and renovate it and stay with mother, they said 1 portion in G floor belongs to him and they will not give.First floor entirely they said they will give to his son who will get married in 2 years -That is not right. Please suggest, how can we fight for our right ?