The sale must be made subject to all payments that may hereafter become due on such contracts, and if there are any such the sale must not be confirmed by the district court until the purchasers execute a bond to the executor or administrator, for the benefit and indemnity of himself and of the person entitled to the interest of the decedent in the lands so contracted for, in double the whole amount of payments thereafter to become due on such contract, with such sureties as the judge of the district court shall approve.