In the cases referred to in Sections 21106 and 21107, the powers and duties conferred and imposed upon the trustee or trustees shall be exercised and performed by the grantor, or by his or her spouse, during his or her life, as the case may be. Upon the death of the grantor, or the surviving spouse, as the case may be, the powers and duties shall devolve upon and shall be exercised by the trustees named in the grant, and their successors.