Land ownership

Sir, I had bought a land of 60x40 from my relative( seller) in mysore and it is registered in my name. My relative ( seller) has a site in front of our site. But later I realised that my site does not have katha. When enquired about this to my relative he said even his own site does not have katha and he will set it right. Later on after few years he said katha has been issued to the both site ( mine and his). But so far he has not given us any documents relating to katha of our site. Last year my relative( seller) called us to persuade us to give our site for joint venture for construction of apartments saying that I can earn profits. I orally consented subject to written agreement done with the builders at the earliest. But he never came to us to get any documents signed regarding joint venture. Last month we are shocked to see the construction reached mid-stage without we signing any contract with builders. But he says he has given our site on behalf of us to builders. He says he has katha done for our site in his name. So can we legally proceed against him?