Mass. Gen. Laws ch. 34 § 12
In case of inability to attend, or interest in a question before the commissioners, or if any part of a highway relative to which they are to act lies within the town where a commissioner resides, the commissioners qualified to act and the clerk of the courts for the county shall appoint one or more persons, not residing in the same town as any commissioner, nor in the same town with each other, if more than one, to act as commissioners in place of those absent or disqualified, until such absence or disqualification ceases. The commissioners may, however, receive a petition, issue an order of notice thereon, take a recognizance, approve bills or payrolls, or perform ministerial acts, whenever two members are competent to act. If they cannot otherwise organize, residence shall not disqualify.
Mass. Gen. Laws ch. 34, § 12