§1. When circumstances require it, the pastoral care of a parish or of different parishes together can be entrusted to several priests in solidum, with the requirement, however, that in exercising pastoral care one of them must be the moderator, namely, the one who is to direct the joint action and to answer for it to the bishop.
§2. If, because of a lack of priests, the diocesan bishop has decided that participation in the exercise of the pastoral care of a parish is to be entrusted to a deacon, to another person who is not a priest, or to a community of persons, he is to appoint some priest who, provided with the powers and faculties of a pastor, is to direct the pastoral care.
Source: Code of Canon Law (Vatican.va)