In all mortgages and deeds of trust of real property wherein two or more persons, as trustees or otherwise, are given power to sell the property therein conveyed or embraced, and one or more of such persons dies, any one of the persons surviving having such power  may make sale of such property in the manner directed in such deed, and execute such assurances of title as are proper and lawful under the power so given; and the act of such person, in pursuance of said power, shall be as valid and binding as if the same had been done by all the persons on whom the power was conferred. (1885, c. 327, s. 2; Rev., s. 1033; C.S., s. 2582; 1967, c. 562, s. 2.)