“In case I shall in my life-time enter into any contracts for the purchase of any lands, tenements, or hereditaments, and I should happen to die before the necessary conveyances thereof are executed, I order and direct, that all and every such contract or contracts so entered into by me as aforesaid, shall be completed and carried into execution by my said trustees after my death, and that the purchase-monies for such respective estates and premises, shall be paid by them, by, with, and out of my personal estate and effects, and that the deeds and conveyances thereto respectively shall be made to them, their heirs, and assigns; and that they, and every of them, shall stand, remain, and be seised, and possessed of all and singular the premises so to be conveyed upon, under, and subject to such and the same