Sale agreement

You cannot buy such property, as it is on loan.  After the seller clears the loan by way of reconveyance of the mortgage deed, you can buy it.

You can take the assistance of an experienced lawyer in the local and obtain his opinion for all such further proceedings in this regard because without knowing the details any opinion rendered here would be a misguidance.

Don't buy this apartment as it's title is not clear. 

Sir actually we planned to tranfer the loan in our name we talked about the sbi manager about the home loan and the be tranfer to the account of seller's loan ac and pay off the loan. 

It is better to avoid purchase of such property.

Howeveer, if you have decided to buy it you should seek professional services of a local prudent lawyer for proper analyses of facts/ documents

Drafting of the proposed agreement rquires perusal of documents as well the discussion of inherent issues. Only a local lawyer is in a position to assist you.