Paul's authority is directly from God, not through the other apostles.
The other apostles recognized his call to the Gentiles, and rejected the necessity of circumcision for believers in Christ.
Paul rightly rebuked Peter for re-segregating meals according to Torah.
We are not reckoned righteous by keeping Torah, but by believing in Jesus as the Christ.
Our requirement to keep Torah, and our condemnation by Torah, was killed with Christ on the cross.
If you try to live (be justified) by the law, you will be condemned by it, for all have sinned. We should live by the promise, which precedes the law. The law doesn't contradict the promise, but wasn't meant as the source of life or justification. Its purpose is rather to define and condemn sin. We are no longer under it, since Christ has come. It is faith in the promise of God to Abraham and to us, not adherence to the Law, that reckons us righteous and one of God's people.