Saledeed buyer is x, land bank record show x & y

As per your statement X only the buyer then his name alone could reflected in the title of the property. How the witness Y name reflected in the title. so better to show the records with local advocate and get clarity. 

Sir ,the Lamd bank record downloaded from development authority shows both X & Y names. Could there be any possibility that after sale deed, Y was also added by X himself in the ownership so maybe the land records reflect both names. It cannot be simply by default, there has to be something that was done which now reflect Y's name. How can i get to know the real ownership details of the property please guide the process .

Without details of records with assumption can not give our reply. so better to consult local lawyer. 

get R.T.I. copy and show to the local lawyer. He will suggest you. 

Sir how can we get the RTI copy can u just tell in brief and where to apply ? In Registrar office or in Development Authority office where land mutation record is maintained?

You can approach a local advocate and get it