The heirs succeeding to such institute or heir in possession as aforesaid shall in like manner as above provided be bound, unless otherwise expressly directed by him, to relieve to the extent aforesaid his executors, or other personal representatives, of all liabilities which he may have undertaken in any contracts or agreements for or with reference to the execution of improvements of the description aforesaid on the mansion-house and offices of the entailed estate, or any other parts of the estate not under lease, and to repay to the extent aforesaid to such executors or other personal representatives any sums of money which they may be called upon to pay and may have paid in virtue of such contracts or agreements.