To Paul, resurrection makes us all sons of God, but Jesus was the first. We see this in Romans 1:4, where Paul tells us Jesus was the Son of God by the fact of his resurrection:
4 And declared to be the Son of God with power, according to the spirit of holiness, by the resurrection from the dead:
Paul promised his followers that they would all be resurrected, saying that the resurrection of Jesus came first and that others would soon follow:
Romans 6:4-5: Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life. For if we have been planted together in the likeness of his death, we shall be also in the likeness of his resurrection:
The Corinthians rejected the idea of a physical resurrection, which is what they thought Paul had been talking about. In 1 Corinthians 15:12-13, he assured them that there would be a resurrection, saying that their faith in the resurrection of Jesus was evidence of that:
1 Corinthians 15:12-13: Now if Christ be preached that he rose from the dead, how say some among you that there is no resurrection of the dead? But if there be no resurrection of the dead, then is Christ not risen:
This now makes the meaning of Romans 8:29 clearer:
For whom he [God] did foreknow, he also did predestinate to be conformed to the image of his Son, that he might be the firstborn among many brethren.
Paul says that Jesus became the son of God by his resurrection, which means he was the "firstborn," but those who were in the general resurrection to come would be "conformed to the image of his Son" - sons of God, but of course not firstborn, because this was Jesus.
The theology of Colossians differs somewhat from that in Paul's undisputed epistles (including Romans and 1 Corinthians), reflecting the general view of critical scholars that Colossians was written in the 70s of the first century and not by Paul himself. Here, Jesus was firstborn because he existed at the time of creation:
Colossians 1:15-18: Who is the image of the invisible God, the firstborn of every creature: For by him were all things created, that are in heaven, and that are in earth, visible and invisible, whether they be thrones, or dominions, or principalities, or powers: all things were created by him, and for him: And he is before all things, and by him all things consist. And he is the head of the body, the church: who is the beginning, the firstborn from the dead; that in all things he might have the preeminence.
It has long been accepted that Hebrews was not written by Paul, although the second-century Church Fathers preserved the book in the belief that Paul had written it. The theology of Hebrews 1:6 is consistent with that in Colossians, except that here Jesus may not have been present at creation, with the angels already there to worship him at his birth:
Hebrews 1:6 And again, when he bringeth in the firstbegotten into the world, he saith, And let all the angels of God worship him.
Hebrews 11:28 would appear to be referring to God's act in killing the firstborn in Egypt during the Captivity and the time of Moses, as we can more readily see by looking at the preceding and following verses, and so has nothing to do with Jesus as firstborn:
Hebrews 11:24-29: By faith Moses, when he was come to years, refused to be called the son of Pharaoh's daughter; Choosing rather to suffer affliction with the people of God, than to enjoy the pleasures of sin for a season; Esteeming the reproach of Christ greater riches than the treasures in Egypt: for he had respect unto the recompence of the reward. By faith he forsook Egypt, not fearing the wrath of the king: for he endured, as seeing him who is invisible. Through faith he kept the passover, and the sprinkling of blood, lest he that destroyed the firstborn should touch them. By faith they passed through the Red sea as by dry land: which the Egyptians assaying to do were drowned.