Land Purchased from Realtor(not actual owner) and realtor died.

Sir/Madam... Myself Rajesh. I'm from ananthapur(AP) In 2012,I purchased a land from realtor(Means-He takes possession of land in acres by giving some money like advance/token payment and divide land into plots & sell). Due to some reasons,main owner of land is unable to register(Because registered property is in his late parents name(Parents died),legal heirs I.e., girls/Women demanding share in property from his brothers).So he unable to register for the buyers. But our seller I.e., realtor died of heart attack before registering property in our name. So we went to his spouse and children's and ask our money back(in polite manner).They are behaving rude and saying that we don't have money & they saying that my husband/father didnt gave money to us.So how can we(Spouse/children) repay to you. And now they are saying that -my husband didn't mention your name as one of the buyer. We showed them deed/agreement also...but they didn't respond. So we have a stamp paper deed worth for 10lakhs. and His business notepad deed worth for 5 Lakhs. Totally -15lakhs. In agreement it is clearly mentioned about the so & so land with ****feets.....,But land was not registered in his name I.e., realtors. So what are my options & if possible how much I get back & how much rate of interest I has to claim....? Please suggest me.....Please