Remember Christ is the head of the church. From among the members, elders and deacons are to be appointed. Notice too that the Bible always speaks of more than one elder over a congregation. Never is there only one elder ruling over them. Neither do you ever have the elders and deacons of one congregation taking control of another congregation.
Congregations are to fellowship one another.
However, they do not exercise control over each other. The words elder , pastor , bishop , shepherd , and presbyter all have reference to the same office. So, an elder is a pastor, a bishop, etc. Moreover he must have a good testimony among those who are outside, lest he fall into reproach and the snare of the devil. Not everyone in the church can be an elder.