Purchase of flat at titawala unable to get the refund

Since you have the sale agreement executed by a registered deed, you could have taken action through legal forums i.e., either by making a complaint with the RERA or with the consumer commission for recovery of your advance amount  for the reasons you rely upon, but before that you should have taken setps to cancel the agreement as demand the return of the advance amount.

Alternately you could have approached civil court with with a suit for specific performance of contract or a suit for recovery of your money owing to the cancellation of the sale agreement.

If you had given money directly to the 1st partner then you may have to lodge a criminal complaint against him alone, there is no point in following it up with the other partner if he is not undertaking any responsibility to return your amount.

Since it is a partnership firm, you can sue the firm along with its partnerrs for recoveyr of your amount.

You consult your advocate and proceed by whichever step that will be convenient to you as suggested