Whoa. You ask good questions brother. When I read the title of the thread I was like, huh, trick question, lol. But reading the post...A slew of scriptures come to mind which validates the question. Without reading the rest of the thread, here I go. This is what came to mind, I'm not saying it is right or wrong, just saying, pondering this question brought these scriptures to mind.
Matthew 18:18
18 Assuredly, I say to you, whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven.
Matthew 28:18
18 And Jesus came and spake unto them, saying, All power is given unto me in heaven and in earth.
Mark 16:
15 And he said unto them, Go ye into all the world, and preach the gospel to every creature.
16 He that believeth and is baptized shall be saved; but he that believeth not shall be damned.
17 And these signs shall follow them that believe; In my name shall they cast out devils; they shall speak with new tongues;
18 They shall take up serpents; and if they drink any deadly thing, it shall not hurt them; they shall lay hands on the sick, and they shall recover.
19 So then after the Lord had spoken unto them, he was received up into heaven, and sat on the right hand of God./
1 Corinthians 2:13-16
13 Which things also we speak, not in the words which man's wisdom teacheth, but which the Holy Ghost teacheth; comparing spiritual things with spiritual.
14 But the natural man receiveth not the things of the Spirit of God: for they are foolishness unto him: neither can he know them, because they are spiritually discerned.
15 But he that is spiritual judgeth all things, yet he himself is judged of no man.
16 For who hath known the mind of the Lord, that he may instruct him? but we have the mind of Christ.
The short answer is yes, God is the only one who can forgive sins unto redemption. But if we believe, and are in Christ, and Christ in us, and are led of the Spirit, it could be loosely said that we can, but it is really Christ in us which effects it. But we are of the body and so in a manner of speaking make it happen, nay, allow it to happen is a better way to say it.
Like the laying on of hands to heal, we cause it to happen but are not the source of the power to do it, yet it couldn't be done without our participation. (It could, but God likes for us to participate). We who have the mind of Christ and walk in Christ play a big part in Gods work here. We have been given authority in Christ, who has been given all authority over this world. We have been give a commission, as were the disciples. Most of our personal authority is to go into the world and preach the gospel message, but in certain instances, it could certainly extend to speaking the forgiveness unto someone.
The forgiveness is certainly our own forgiveness from our own heart unto another, which is within the will of God. If you bind this upon earth, it will certainly be bound in heaven. We have to understand and walk in the fact that this is in love, and is an attribute of becoming love, as is God and that we shall walk in it. This does not mean that we have the authority to go around condemning people. This would be a dangerous perspective to hold for with what judgment we mete out, it shall be measured unto us again. For us to be able to righteously condemn another would be a situation which would not arise often if at all because God is not willing that any should perish and His love covers a multitude of sins. Something that the carnal mind cannot grasp.
I think. lol.