Biyana deed letter

There is a 10 marla old house and the owner made a deal with a party to sell 10 marla house to them.
That party paid them a biyana and afterwards could not pay the full amount with in that time period. They could only pay half of the price. Now the owner has offered me to buy 5 marla out of it and the rest of the 5 marla will be given to that party.

My question is that should i ask the owner to first legally cancel the biyana deed?

What is the legal procedure to buy this property?

Thank you very much for the clarification. Actually the house was built on two five marla plots. Location is Lahore old rifle range.

The biyana deal is time barred.

Will there be any legel problem to buy one plot in such situation?