Land ownership

I think your relatives might have been sold the land without informing you.  So ask your relatives to register the sale deed in your favour by paying the remaining amount if any as you both mutually agreed.

You need sale deed to transfer the ownership of land. IF your relatives received the payment and the receipt is there then file suit for specefic performance. If they have already sold the land then better to get your money back and or file complaint for fraud

@kavksatyanarayana and @real soul thank you for the answer . As I know it's not only our land but it includes land from other 3 peoples which really belongs to them have been registered in one person's name. I think our relatives have not sold the land without our knowledge. It's a ancestral property. In current situation what is the actual legal method to get the ownership of land . We are living in that house from 1997 and we have paid the property tax from since.

Get a registered deed in your favour from your relatives. 

File declaratory suit with relevant documents against them.