This is one human who has sinned against anther asking that brother for forgiveness.
16But if he will not hear thee, then take with thee one or two more, that in the mouth of two or three witnesses every word may be established.
Here that same brother is told to take one or two more. No mention of them being any more than a brother or sister in Christ.
17And if he shall neglect to hear them, tell it unto the church: but if he neglect to hear the church, let him be unto thee as an heathen man and a publican.
Here he is told to take it before the church, his local group of brothers and sisters in Christ. The church has no duty other than being a witness that he tried to get the other brother to forgive him. The church forgives no one because they weren't the ones being asked to forgive. The brother has done all he can so that sin is loosed from him even though the other brother didn't forgive him. He is no longer responsible for it. The unforgiving brother has his sins against God bound by his un forgiveness
18Verily I say unto you, Whatsoever ye shall bind on earth shall be bound in heaven: and whatsoever ye shall loose on earth shall be loosed in heaven.