Matthew, John, and Peter were of course among Jesus’ twelve apostles. Paul rightly claimed apostolic authority because of the special resurrection appearance that Jesus granted him on the road to Damascus, and Mark and Luke derived their traditions predominantly, at least initially, from Peter and Paul respectively, so at least says strong early church tradition. We have already seen how people like James and Jude would have been half brothers of Jesus, not necessarily believers during his earthly life, but certainly eyewitnesses of portions of his life and recipients of resurrection appearances in ways that persuaded them subsequently of the legitimacy of his claims. That leaves only the author of Hebrews who remains disputed, but both in the ancient and modern worlds debates surrounded whether or not this was Paul or a close companion of Paul and no other candidates were ever seriously suggested.
This statement on authors is closely connected to Blomberg’s criteria for New Testament canonicity.