Subject to the provisions of this and the special Act, it shall be lawful for the promoters of the undertaking to agree with the owners of any lands by the special Act authorized to be taken, and which shall be required for the purposes of such Act, and with all parties having any right or interest in such lands, or by this or the special Act enabled to sell and convey the same, for the absolute purchase of any such lands, or such parts thereof as they shall think proper, and for the purchase of all rights and interests in such lands of what kind soever.