This is an unofficial version of a Massachusetts General Law.
Section 3-717
If 2 or more persons are appointed co-representatives and unless the will provides otherwise, the concurrence of all is required on all acts connected with the administration and distribution of the estate. This restriction shall not apply when any co-representative receives and receipts for property due the estate, when the concurrence of all cannot readily be obtained in the time reasonably available for emergency action necessary to preserve the estate, or when a co-representative has been delegated to act for the others. Persons dealing with a co-representative if actually unaware that another has been appointed to serve or if advised by the personal representative with whom they deal that the personal representative has authority to act alone for any of the reasons mentioned herein, are as fully protected as if the person with whom they dealt had been the sole personal representative.