If you are going to read the gospels into the epistles it is you that has to be consistent. You conflate apostles with disciples, and you assume that the epistle writers were writing about a preacher from Galilee when they make no such claim. Paul is an apostle no different than the apostles that he meets, the only problem he has is convincing them that he no longer persecutes those from the church of God, that is the past that he has to deal with, he states as much. According to Paul, the risen Christ made an appearance, he had visions, and his experience of that was no different than the other apostles and brethren that also had visions of a risen Christ.Now you're using the Gospels and Acts to contradict Paul, who is the earlier source? Is that only OK when it seems to support your position?
Of course, the later tradition is that Jesus didn't have biological brothers at all and that ἀδελφός is supposed to mean something else (never mind that the context doesn't really allow for it). The erasure of his earthly family is a process we can trace.