Michigan Compiled Laws, Chapter 700. Estates and Protected Individuals Code § 700.2903

Sec. 2903. (1) A disclaimer is not valid unless it complies with all of the following:

(2) If a disclaimable interest is disclaimed by a fiduciary on behalf of the person to whom the disclaimable interest devolves, the disclaimer must be signed by all incumbent fiduciaries. Unless the governing instrument requires otherwise, a disclaimer of a disclaimable interest by a trustee may be signed by less than all incumbent trustees. A disclaimer of a fiduciary power by a fiduciary may be signed by less than all incumbent fiduciaries.